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Companion  Texts  to  4:his  Outline 


INORGANIC   CHEMISTRY 


BY 

ALEXANDER  SMITH 


780  +  XVIIIpp.     With  106  Figures 

Octavo,  $2.25  net 


GENERAL   CHEMISTRY 
FOR   COLLEGES 

BY 
ALEXANDER  SMITH 


531  +XIII  pp.      With  67  Figures 

Octavo,  $2.15  net 


NEW  YORK.  THE  CENTURY  CO. 
LONDON.  GEO.  BELL  AND  SONS 


A  LABOEATORY  OUTLINE  OF 
GENERAL  CHEMISTRY 


BY 

ALEXANDER   SMITH 
« , 

PROFESSOR  OF  CHEMISTRY   IN  THE   UNIVERSITY   OF  CHICAGO 

jfourtb  3E£>ttfon. 

REVISED  IN  COLLABORATION  WITH 

WILLIAM  J.   HALE 

ASSISTANT  PROFESSOR  OF  CHEMISTRY  IN  THE 
UNIVERSITY   OF  MICHIGAN 


r> 

TWENT  Y-SIXTH 


NEW  YORK 
THE  CENTURY  CO. 

1910 


<r 


COPYRIGHT,  1907,  BY  THE  CENTURY  Co. 


COPYRIGHT,  1899,  BY  ALEXANDER  SMITH 


Set  up  and  electrotyped  June,  1899 

Reprinted  September,  1900 
Second  Edition,  Revised,  October,  1902 

Reprinted  August,  1905 

Third  Edition,  Revised,  June,  1907 

Fourth  Edition,  Revised,  January,  1908 

Reprinted  August,  1908 

Reprinted  April,  1909 

Reprinted  January,  1910 


Stanbope  press 

H.   OIL.60N   COMPANY 
BOSTON,   U.  6.  A. 


PREFACE  TO  THE  THIRD  EDITION 

THE  extensive  use  of  the  previous  editions  seems  to  have 
shown  the  acceptability  of  the  general  plan  of  the  book.  This 
conclusion  has  been  confirmed  by  the  fact  that  the  second 
edition  has  been  translated  into  German,  and  that  a  transla- 
tion of  the  present  one  into  Russian  is  being  prepared.  In  the 
present,  therefore,  the  fundamental  features  of  the  previous 
edition  have  been  preserved.  In  brief,  the  aim  has  been  to 
furnish  the  basis  for  a  systematic,  coherent,  and  instructive 
study  of  the  elements  of  chemistry  from  the  modern  stand- 
point. 

In  the  effort  to  make  misapprehensions  and  mistakes  as 
nearly  impossible  as  may  be,  the  directions  have  been  entirely 
rewritten,  and  in  many  cases  have  been  amplified,  and  a  num- 
ber of  the  experiments  have  been  modified.  An  entirely  new 
set  of  figures  has  also  been  drawn.  To  render  the  exercises  more 
instructive,  and  still  further  to  discourage  mechanical  work,  a 
larger  number  of  questions  has  been  inserted.  With  the  same 
end  in  view,  data  in  regard  to  solubility  have  been  introduced 
(Appendix)  as  a  new  feature,  and  their  use  hi  explaining 
chemical  phenomena  has  been  illustrated  in  many  experiments. 
The  rationalizing  value  of  using  the  conceptions  of  chemical 
dynamics,  the  electromotive  series,  and  the  degrees  of  ioniza- 
tion  has  been  emphasized  by  more  frequent  references. 

Some  of  the  formal  quantitative  experiments  have  been 
modified,  and  the  directions  have  been  made  clearer.  The 
value  of  these  experiments  has  been  found  to  lie  chiefly  in  the 
basis  they  give  for  clear  understanding  of  the  difficult  subject 
of  combining,  atomic,  and  molecular  weights. 

When  quantitative  experiments  were  first  used  in  elementary 
chemistry  it  was  hoped  that  they  would  also  assist  in  develop- 
ing an  abiding  realization  of  the  quantitativeness  of  all  chem- 
ical phenomena  and,  as  a  consequence,  make  all  the  thought 
and  work  of  the  student  more  rigorous.  In  the  experience  of 
the  authors,  however,  quantitative  experiments  of  the  usual 
kind  fail  to  accomplish  this  important  result.  Students  who 
have  performed  such  experiments  still  add  a  test-tube  full  of 
sulphuric  acid  to  a  liquid  known  to  contain  only  a  trace  of 
a  compound  of  lead,  and  still  think  less  than  a  dozen  bubbles 
of  hydrogen  sulphide  sufficient  to  precipitate  the  lead  from 

M88208 


vi         PREFACE  TO   THE  THIRD   EDITION 

10  cc.  of  approximately  normal  lead  nitrate  solution  (see  74  g 
and  note  36,  p.  67).  They  attempt  to  make  potassium  chlorate 
without  considering  that  a  few  bubbles  of  chlorine  (perhaps 
liberally  mixed  with  air)  will  not  saturate  three  grams  of 
potassium  hydroxide  (see  57  a),  or  they  take  too  much  water 
and  then,  not  having  considered  the  solubilities  and,  therefore, 
not  knowing  what  is  wrong,  throw  away  the  product  and  lose 
valuable  time  by  starting  entirely  ab  initio.  The  failures 
which  result  from  this  lack  of  a  sense  of  quantity  are  innum- 
erable, and  the  discouragement  often  a  serious  hindrance  to 
ultimate  success.  The  fault,  of  course,  is  in  the  instruction, 
and  the  remedy  lies  in  exercises  and  questions  devised  to  cul- 
tivate this  missing  sense.  It  is  to  meet  this  situation  that  the 
tables  of  solubilities  have  been  introduced  and  have  been 
referred  to  frequently  (see,  e.g.,  64,  65, 126  a,  127, 137  c-f,  139  d). 
With  the  same  object,  the  tables  of  degrees  of  ionization  have 
been  utilized  (see  e.g.,  64,  66),  and  the  varying  degrees  of 
activity  of  acids  have  been  observed  (e.g.,  164)  and  measured 
(120).  Still  further  to  cultivate  rational  experimentation,  the 
solutions  on  the  side-shelf  should  be  approximately  normal 
(or  in  simple  multiples  or  submultiples  of  this  concentration), 
and  the  student  may  then  be  led  to  note  the  concentrations 
and,  in  many  experiments,  to  take  suitable  quantities  accord- 
ingly. The  importance  of  the  point  of  view  indicated  in  the 
foregoing  can  hardly  be  overestimated.  Genuine  success  in 
business  or  in  the  professions,  and  often  even  the  mere  making 
of  a  livelihood,  depend  so  largely  on  ability  to  reason  quanti- 
tatively that  practice  in  this  kind  of  reasoning  is  of  inestimable 
value  in  education.  If,  on  the  contrary,  the  work  in  chemistry 
is  purely  haphazard  in  this  respect,  the  study  of  the  science 
may  easily  be  a  positive  detriment  rather  than  a  benefit,  and 
that  whether  the  student  ultimately  makes  direct  use  of  his 
knowledge  of  the  science  or  not. 

If  it  appears  that  these  changes  have  made  the  work  more 
difficult,  it  must  be  remembered  that  valuable  knowledge  can 
be  obtained  only  by  effort,  and  that  the  value  of  the  knowledge 
is  in  proportion  to  the  effort,  provided  the  latter  is  directed 
rationally  along  instructive  lines.  Easy  chemistry  must  be 
superficial  and  empirical,  in  proportion  to  its  simplicity.  It 
is  easy  to  perform  experiments  mechanically;  it  is  necessarily 
more  difficult  to  interpret  the  results  and  extract  all  that  they 
can  teach. 

The  book  is  intended  for  beginners  in  colleges,  universities, 
and  professional  schools.  It  must  be  understood,  however, 
that  no  one  class  is  expected  to  perform  all  the  experiments. 


PREFACE  TO   THE   THIRD   EDITION         vii 

Only  from  one-half  to  three-quarters  of  the  whole  material  can 
be  covered  in  thirty-three  weeks,  by  a  student  working  four  to 
six  hours  a  week.  The  authors  have  found  no  difficulty  in 
arranging  a  course  only  twelve  weeks  long,  and  utilizing  con- 
siderably less  than  half  the  contents.  The  outline  is  subdivided 
into  numerous  small  paragraphs,  so  that  each  instructor  may  be 
able  to  make  such  a  selection  as  will  suit  the  work  he  desires 
to  give.  It  is  hoped  that  the  whole  body  of  material  is  suffi- 
ciently great  to  permit  the  arrangement  of  a  course  of  almost 
any  character.  Thus,  many  or  few  quantitative  experiments 
may  be  given,  and  many  or  few  theoretical  matters  illustrated. 
Emphasis  may  be  laid  on  work  leading  to  analysis,  or  some 
of  that  work  may  be  sacrificed  in  order  to  include  a  larger 
number  of  preparations.  The  student  may  even  be  directed 
in  certain  paragraphs  to  ignore  the  questions.  Finally,  the 
order  of  the  experiments  may  be  altered  without  serious  dis- 
turbance. 

The  recent  great  improvement  in  the  work  in  chemistry  hi 
secondary  schools  makes  it  desirable  to  recognize  and  encour- 
age this  work  by  outlining  a  different  selection  of  experiments 
for  those  who  have  studied  the  science  before,  and,  if  possible, 
to  give  such  students  separate  class-room  instruction. 

Sample  selections  of  experiments  for  beginners  and  for  more 
advanced  students  have  been  given  in  a  separate  pamphlet, 
which  will  be  sent  to  instructors,  upon  request,  by  -publishers. 
This  pamphlet  includes  also  lists  of  apparatus  and  chemicals 
and  other  data  helpful  in  the  organization  of  the  laboratory 
instruction. 

In  the  preparation  of  this  edition  the  authors  have  received 
helpful  suggestions  from  Prof.  S.  Lawrence  Bigelow  of  the 
University  of  Michigan,  from  Prof.  Ralph  H.  McKee  of  Lake 
Forest  University,  and  from  Prof.  H.  N.  McCoy,  Dr.  C.  M. 
Carson,  and  Mr.  T.  B.  Freas  of  the  University  of  Chicago, 
as  well  as  from  many  others.  We  wish  here  gratefully  to 
acknowledge  the  improvements  which  the  Outline  owes  to 
these  suggestions. 

THE  AUTHORS. 

CHICAGO  AND  ANN  ARBOB, 
May,  1907 


PREFACE  TO  THE  FOURTH  EDITION 

THE  third  revised  edition  having  been  exhausted  within  a  few 
months  of  its  publication,  the  opportunity  is  taken  to  introduce 
some  needed  alterations.  Aside  from  a  few  corrections,  only 
one  considerable  change  is  made.  This  consists  in  the  transfer 
of  Chapter  V  of  the  last  edition  bodily  so  that  it  follows  Chapter 
VII  of  the  same  edition.  This  places  the  quantitative  experi- 
ments on  equivalent  weights  after  the  work  on  water,  chlorine 
and  hydrogen  chloride  instead  of  before  it.  In  the  "  Introduc- 
tion to  General  Inorganic  Chemistry,"  to  which  the  Outline  is  a 
companion  volume,  the  discussions  of  molecular  and  atomic 
weights  and  of  the  atomic  hypothesis  occur  at  this  point  and  are 
therefore  now  contemporaneous  with  the  quantitative  experi- 
ments dealing  in  part  with  the  same  subjects.  Thus  there  have 
been  adjusted  the  two  difficulties  in  making  a  convenient  scheme 
of  work,  which  were  formerly  occasioned  by  the  lack  of  laboratory 
work  to  accompany  the  molecular  and  atomic  hypotheses  and 
their  applications,  and,  at  a  different  stage,  the  great  excess  of 
laboratory  work  over  class-room  work  at  the  time  when  the  main 
set  of  quantitative  experiments  was  being  performed.  Many 
instructors*  will  feel  that,  apart  from  this  mere  matter  of  peda- 
gogical convenience,  the  postponement  of  the  quantitative 
work  is  in  itself  advantageous,  because,  after  more  laboratory 
experience,  greater  ease  of  performance  and  greater  accuracy  in 
results  may  now  reasonably  be  expected. 

This  opportunity  may  be  taken  to  call  attention  to  the 
change  in  the  nomenclature  of  ionic  substances  (p.  55)  in 
Chapter  X  et  seq.  This  considerable  departure  from  the  system 
used  in  the  text-book  was  made  only  after  careful  considera- 
tion. The  nomenclature  now  employed  in  the  outline,  although 
it  has  been  developed  chiefly  since  the  text-book  was  written, 
has  already  come  into  fairly  consistent  use  in  American  chemi- 
cal literature.  In  Great  Britain  no  one  system  has  established 
itself.  In  Germany  a  plan  similar  to  that  here  adopted  has  been 
used  by  Ostwald  and  others  for  several  years. 

THE  AUTHORS. 

November,  1907. 


viii 


CONTENTS 

CHAPXEBS  PAGES 

GENERAL  INSTRUCTIONS      1 

I.  MANIPULATION , 3 

II.  CHARACTERISTICS  OF  CHEMICAL  PHENOMENA.    ...  9 

III.  OXYGEN 14 

IV.  HYDROGEN 19 

V.  WATER  AND  SOLUTION 23 

VI.  CHLORINE  AND  HYDROGEN  CHLORIDE 29 

VII.  EQUIVALENT  WEIGHTS,  FORMULA,  EQUATIONS  ...  33 
VIII.   BROMINE,  IODINE,  FLUORINE,  AND  THEIR  COMPOUNDS 

WITH  HYDROGEN 41 

IX.   DOUBLE  DECOMPOSITION.     OXYGEN  COMPOUNDS  OF 

THE  HALOGENS.     HYDROGEN  PEROXIDE     ....  48 
X.  loNlZATION   AND   INTERACTIONS   OF  ACIDS,   BASES, 

AND  SALTS 55 

XI.   SULPHUR 65 

XII.  THE  ATMOSPHERE,  NITROGEN,  AMMONIA    .....  76 

XIII.  OXIDES  AND  OXYGEN  ACIDS  OF  NITROGEN    ....  81 

XIV.  PHOSPHORUS ' • .  87 

XV.   CARBON  . 90 

XVI.   THE  ACTIVITY  OF  ACIDS  MEASURED  CHEMICALLY    .  96 

XVII.   SILICON  AND  BORON 98 

XVIII.    METALLIC  ELEMENTS  OF  THE  ALKALIES 100 

XIX.   METALLIC  ELEMENTS  OF  THE  ALKALINE  EARTHS.    .  107 

XX.   COPPER  AND  SILVER Ill 

XXI.  MAGNESIUM,  ZINC,  CADMIUM,  MERCURY 116 

XXII.  ALUMINIUM,  TIN,  LEAD 120 

XXIII.  ARSENIC,  ANTIMONY,  BISMUTH 123 

XXIV.  CHROMIUM,  MANGANESE      126 

XXV,   IRON,  COBALT,  NICKEL 129 

APPENDIX  .  132 


GENEKAL  INSTRUCTIONS. 

NOTES  1-17. 

Read  the  "Regulations"  posted  in  the  laboratory.  Read  also, 
attentively,  the  following  notes: 

Note  1.  —  Provide  yourself  with  a  note-book  and  make  a  careful 
permanent  record  immediately  after  each  experiment.  Enter  the 
numbers  and  titles  of  the  paragraphs  of  the  outline  systematically. 
State  (1)  what  you  did,  if  anything  beyond  the  directions,  but  do 
not  copy  the  printed  directions  themselves,  (2)  what  you  observed, 
(3)  what  conclusions  you  drew.  A  sketch  of  the  apparatus  will 
enable  you  to  recall  the  circumstances  of  the  experiment,  if  later 
reference  to  it  is  necessary.  This  note-book,  when  called  for,  is 
to  be  handed  in  for  inspection. 

The  blank  pages  in  this  Outline  are  not  intended  for  the  final 
notes.  They  may  be  used  for  individual  suggestions  given  by 
the  instructor,  preliminary  notes,  record  of  weighings,  etc. 

The  directions  have  been  expressed  with  the  utmost  care  and 
brevity.  Every  word  is  significant.  Italics  are  therefore  nowhere 
employed  for  the  purpose  of  emphasis. 

Note  2.  —  Whenever  an  interrogation  point  or  a  direct  ques- 
tion appears  a  corresponding  note  should  appear  in  the  note-book. 
The  "  (?)"  indicates  something  to  be  observed  and  recorded. 

Note  3.  —  The  very  numerous  questions  asked  in  the  course  of 
this  outline  are  intended  to  be  answered,  not  by  speculation,  but 
by  careful  observation  and  reasoning  based  on  the  results  of  this. 
Very  often  the  student  will  find  it  necessary  to  devise  and  carry 
out  further  experiments  of  his  own  before  a  satisfactory  answer  is 
obtained.  When  a  question  occurs  to  you,  endeavor  by  reflection 
and  study  to  answer  it  yourself  before  consulting  an  instructor. 

Note  4.  —  In  many  cases  the  work  outlined  could  not  in  itself 
furnish  the  basis  for  an  answer,  and  fuller  investigation  of  the 
point  would  require  work  beyond  the  time  or  ability  at  the  dis- 
posal of  the  beginner.  Such  questions  are  distinguished  by  an  [R], 
indicating  that  Reference  to  some  authority  (lecture,  book,  or 
assistant)  must  be  made.  The  number  following  the  R  is  that  of 
the  page  in  Alexander  Smith's  Introduction  to  General  Inorganic 
Chemistry,  where  the  necessary  information  may  be  obtained. 
The  authority  should  be  consulted,  however,  only  after  the  experi- 
ments have  been  made  and  the  notes  written  up  as  far  as  possible. 
Note  5.  —  When  a  chemical  change  has  been  observed  the 
equation  should  always  be  given  in  the  notes,  but  an  equation 
alone  is  never  a  sufficient  record. 

Note  6.  —  Where  the  word  [Instructions]  appears,  consult  the 
instructor  before  going  further. 

Note  7.  —  In  quantitative  experiments,  marked  [Quant.],  use  the 
finer  balance,  in  all  other  cases  the  rough  scales  in  the  laboratory, 

Note  8.  —  The  expression  [Storeroom]  indicates  that  the 
sary  apparatus  is  not  included  in  the  individual  outfits. 

1 


2  NOTES  1-17 

Note  9.  —  When  the  word  [Hood]  appears,  the  operation  is  not 
to  be  conducted  at  the  desk  in  the  open  laboratory.  The  appara- 
tus is  to  be  at  once  transferred  to  the  hood  provided  for  operations 
involving  ill-smelling  gases  or  vapors. 

Note  10.  — Where  exact  quantities  are  not  indicated,  very  small 
amounts  of  solutions  (1  c.c.  or  less)  should  be  taken.  This  advice 
is  given,  partly  to  secure  saving  of  material,  but  chiefly  to  avoid  the 
waste  of  time  which  working  with  large  quantities  always  entails. 

Note  11.  — To  obtain  the  necessary  chemical  substances,  do 
not  carry  the  bottles  from  the  side-shelf  to  the  desk.  Bring  a  clean 
test-tube  for  liquids  and  a  watch-glass  for  solids.  For  the  latter, 
a  piece  of  the  paper,  provided  near  the  side-shelf,  may  also  be 
used.  When  too  much  of  any  reagent  has  been  taken,  do  not 
return  it  to  the  bottle. 

Note  12.  —The  chemicals  are  divided  into  two  sets,  each 
arranged  alphabetically  according  to  the  scientific  names.*  The 
first  set  consists  of  solids  in  small  bottles,  the  second  of  liquids. 
The  bottles  and  their  places  are  numbered  consecutively  to  facili- 
tate accurate  replacement,  and  scrupulous  care  must  be  takeft  not 
to  disarrange  them.  Read  the  labels  attentively,  as  there  are 
frequently  several  kinds  of  the  same  substance  (e.g.,  pure,  and 
commercial,  dilute,  concentrated,  and  normal). 

All  materials  are  supplied  through  the  storeroom  service.  Do 
not  therefore  take  side-shelf  bottles,  when  found  empty,  to  the 
instructor,  but  to  the  storekeeper  for  refilling. 

Note  13.  —  The  expression  [From  Instructor],  however,  indi- 
cates one  of  a  few  special -substances  for  which  the  student  must 
apply  to  an  instructor. 

Note  14.  —  The  nine  bottles  on  the  desk  contain  aqueous 
solutions  of  sodium  hydroxide,  sodium  carbonate,  and  ammonium 
hydroxide,  which  are  not  to  be  found  on  the  side-shelves,  and 
sulphuric,  hydrochloric,  and  nitric  acids  in  concentrated  and  dilute 
form.  These  acids  are  all  commercial.  The  corresponding  pure 
concentrated  and  dilute  acids  will  be  found  on  the  side-shelf,  but 
are  to  be  used  only  when  the  outline  so  directs. 

Note  15. — When  any  acid  gets  upon  the  clothing,  apply 
ammonium  hydroxide  solution  [On  desk]  at  once. 

Note  16.  —  Burns,  whether  caused  by  contact  with  hot  objects, 
by  acids,  or  by  corrosive  liquids  like  bromine,  are  rubbed  gently 
with  a  paste  of  sodium-hydrogen  carbonate  and  water.  All  burns, 
save  the  slightest,  must  afterwards  be  dressed  with  an  aqueous 
solution  of  boric  acid  (half -saturated)  [Side-shelf]  to  prevent  infec- 
tion. Obtain  the  assistance  of  an  instructor. 

Cuts  must  be  washed  in  running  water  and  dressed  with  boric 
acid  as  above,  or  with  lanolin  containing  2  per  cent  of  boric  acid. 

Note  17.  —  All  students  work  independently,  except  where 
cooperation  of  two  students  is  expressly  directed. 

*  A  pamphlet  containing  lists  of  the  chemicals  and  apparatus  re- 
quired will  be  furnished,  on  application,  by  the  publishers. 


LABORATORY  OUTLINE 


CHAPTER^. 

MANIPULATION. 


1.  The  Outfit  of  Apparatus.     As  articles  missing  or  found 
imperfect  when  the  course  is  completed  will  be  charged  for, 
check  the  outfit  of  apparatus  carefully  by  comparison  with  the 
list.     To  do  this,  put  all  the  articles  on  the  top  of  the  desk  and 
make  a  mark  on  the  margin  of  the  list  opposite  to  the  names 
of  such  as  you  are  able  to  identify,  at  the  same  time  returning 
the  article  to  the  cupboard  or  drawer.     With  the  assistance  of 
an  instructor,  the  remaining,  unfamiliar  articles  can  then  be 
checked  also. 

2.  Instructions. 

a.  Read  the  general  instructions  and  notes  preceding  this 
chapter  very  carefully,  and  do  not  fail  to  observe  them. 

b.  The  number  of  blast-lamps  and  balances  being  limited, 
the  whole  class  cannot  perform  the  experiments  in  this  chapter 
simultaneously  in  the  order  given.     The  order  is,  in  any  case, 
a  matter  of  indifference.     Two  students  from  the  group  under 
each  assistant  will  begin  with  glass-working  (4)   or  weighing 
(6  and  7  a  and  6).    The  other  students  will  meanwhile  per- 
form 3,  6,  and  7  d  at  the  desks. 

c.  Record  in  the  note-book  the  results  of  3,  6,  and  7  only. 

3.  Bunsen  Burner. 

a.  Attach  the   Bunsen   burner  by  means  of  rubber  tubing 
to  a  gas  connection,  close  the  air-holes  at  the  base,  and  light. 
Now  open  the  air-holes  gradually  and  note  the  effect  upon  the 
flame  (?).     What  is  the  proximate  cause  of  the  difference  in  the 
two  flames  ?    When  using  the  burner  for  heating  purposes, 
always  regulate  the  air  supply  so  as  to  get  a  noiseless,  non- 
luminous  flame. 

b.  Determine  the  structure  of  each  kind  of  flame.     Which 
parts  are  relatively  hotter,  and  which  cooler?    This  may  be 
ascertained  by  observing  the  quality  of  the  glow  produced  in  a 
platinum  wire  held  across  the  flame  in  several  positions.     A 
match-stick  quickly  inserted  may  also  indicate  the  cooler  portions. 
Make  sketches  showing  the  real  form  of  the  flame  (?).     Where 
should  you  hold  an  object  in  the  non-luminous  flame,  in  order 

8 


4  MANIPULATION  [§  4 

to  get  the  greatest  heating  effect?  Prove  the  presence  of  un- 
burnt  gas  in  the  inner  cone  by  inserting  therein  one  end  of  a 
narrow  glass  tube,  and  igniting  the  gas  that  issues  from  its 
uppers  end. .  Which  region  is  deficient  in  oxygen  and  which  has 
an  excess?  .  cThe  <f6rmer  is  called  the  reducing,  the  latter  the 
oxidizing  region. 

«  5.«  'l^ringfroin.the-  side-shelf,  in  a  watch-glass  [Note  12,  p.  2], 
&  small  J  quantity  of  borax  3*  (sodium  tetraborate).  Heat  your 
platinum  wire,  which  has  been  inserted  into  the  fused  end  of  a 
glass  rod,  and  immerse  the  glowing  end  of  the  wire  in  the  borax. 
Use  the  wire  in  straight  condition,  without  any  loop.  Now, 
hold  the  wire  in  the  flame,  observe  the  behavior  of  the  borax, 
and  explain  [R  528.  See  Note  4,  p.  1].  The  bead  must  be  small 
to  avoid  its  dropping  off. 

d.  Bring  the  hot  borax  bead  in  contact  with  a  minute  particle 
of  manganese  dioxide  [Notes  11  and  12],  heat  in  the  flame  near 
the  outer  edge  until  the  particle  has  dissolved,  and  observe  the 
color  of  the  bead  when  cold.     If  the  bead  is  opaque,  too  much 
of  the  dioxide  has  been  taken:  throw  the  molten  bead  off  and 
start  again. 

e.  Cut  off  the  gas  supply  until  the  flame  is  about  6  cm.  in 
height.     Close   the  air-holes  until   a  luminous  point   appears 
at  the  apex  of  the  inner  cone,  and  hold  the  bead  containing  the 
manganese  dioxide  steadily  in  this  luminous  (reducing)  portion. 
Before  withdrawing  the  bead,  lower  it  into  the  inner  cone  of 
unburnt  gases  to  cool.     Observe  the  color  of  the  bead  (?). 

/.    Reheat  the  bead  in  the  oxidizing  part  of  the  flame  (?). 
4,    Glass -Working     [Blast-Lamp    Table.     Instructions,   and 
Note  18,  below]. 

a.  Cut  a  small  piece  off  the  wide  soft  glass  tubing  and  make 
a  test-tube  out  of  it. 

b.  Make  a  test-tube  of  hard  (?  [R  607])  glass. 

c.  Connect  two  pieces  of  narrow  glass  tubing  to  make  a 
longer  piece. 

d.  Make  a  T-tube  by  connecting  two  pieces  of  narrow  glass 
tubing  at  right  angles  to  each  other. 

Note  18.  —  To  cut  narrow  glass  tubing  make  a  slight,  trans- 
verse scratch  with  the  triangular  file.  Hold  the  tubing  so  that 
the  points  of  the  thumbs  are  together  opposite  to  the  scratch,  and 
press  forward  with  the  thumbs  so  as  to  bend  the  tube  away  from 
this  mark.  Wide  tubing  may  be  cut  by  making  a  deep  scratch 
completely  round  the  tube  and  starting  the  crack  by  touching  with 

*  In  this  Outline  the  common,  or  popular  names  are  often  used 
intentionally.  The  systematic  names  must,  in  such  cases,  be  found 
by  the  student  [B]. 


§  5]  MANIPULATION  5 

the  red-hot  end  of  a  glass  rod.  Other  methods  may  be  shown  by 
the  instructor. 

Always  round  off  (fire-polish)  the  sharp  edges  of  freshly  cut 
tubes  by  softening  in  the  Bunsen  flame  (why  do  the  edges  become 
rounded?).  In  the  case  of  test-tubes,  and  other  tubes  of  wide  bore 
in  which  corks  are  to  be  inserted,  the  mouth  must  be  strengthened 
and  rendered  fit  for  receiving  the  cork.  To  accomplish  this,  heat 
the  edge  in  the  flame  and  spread  it  slightly,  but  uniformly,  by 
rotating  in  it  a  pointed  piece  of  charcoal,  or  by  turning  outward 
the  softened  edge  with  the  reverse  end  of  a  file. 

In  making  test-oubes  and  in  connecting  pieces  of  tubing,  distend 
the  softened  parts  by  blowing  immediately  before  allowing  to  cool, 
otherwise  cracks  are  likely  to  appear. 

To  bend  glass  tubing,  never  use  the  Bunsen  flame  (why  ? 
Note  3).  Always  employ  an  ordinary,  flat,  luminous  flame  of 
fish-tail  form.  Hold  the  tubing  lengthwise  in  the  flame,  not  across 
it  (why?),  turning  the  tube  slowly  round  its  axis  to  receive  uniform 
heating.  Keep  the  tube  straight  until  it  is  soft  enough  to  bend  by 
its  own  weight.  Finally,  do  not  actually  make  the  bend  while  the 
tube  is  in  the  flame,  but  after  removal  from  it  (why?). 

Hold  a  piece  of  tubing  in  the  Bunsen  flame,  without  rotating  the 
tube,  and  bend  it  while  it  is  in  the  flame  (?).  Compare  the  bend 
with  one  made  in  the  proper  way  and  account  for  the  difference. 

6.  Construction  of  a  Wash-Bottle.  Select  a  good  cork  which 
will  fit  the  mouth  of  the  largest  flask  and  soften  it  by  rolling 
under  the  foot  upon  the  floor  while  pressure  is  cautiously  ap- 
plied. Bore  two  parallel  holes  with 
the  cork-borer,  and  smooth  them 
by  means  of  a  rat-tail  file  [Note  19, 
below].  Bend  two  pieces  of  glass 
tubing  as  indicated  in  Fig.  1  [Note 
18],  fire-polish  their  edges  and  insert 
them  in  the  openings  in  the  cork. 
Make  the  nozzle  by  softening  a 
piece  of  glass  tubing  in  the  Bunsen 
flame,  drawing  it  to  capillary  dimen- 
sions after  removal  from  the  flame, 
cutting  (6-8  cm.  long),  and  fire- 
polishing.  Connect  the  nozzle  by 
means  of  a  short  piece  of  rubber  Fig.  x 

tubing.    Test  the  apparatus  to  see 

that  it  is  air-tight  [Note  20].  Finally,  fill  the  flask  with  distilled 
water  [Note  21]. 

Note  19.  —  The  cork  borer  is  usually  made  of  brass,  and  the 
edge  is  easily  turned.  Form  the  habit  of  examining  the  edge  and 
freshening  it  by  cautious  application  of  a  triangular  file  [Instruc- 
tions. Note  6]  every  time  it  is  to  be  used.  Do  not  hold  the  cork 


6  MANIPULATION  [§  6 

against  the  table  while  boring,  as  the  edge  of  the  tool  may  be 
ruined.  Hold  the  cork  in  the  hand  and  bore  from  the  narrow  end 
with  care,  exactly  parallel  to  the  axis.  If  the  cork  and  borer  are 
rotated  round  their  axes  and  the  edge  is  fresh,  very  little  force  will 
be  required.  The  borer  is  purposely  chosen  so  as  to  be  smaller 
than  the  tubing.  Its  use  thus1  permits  the  enlarging  and  smoothing 
of  the  hole  with  the  rat-tail  file  until  a  perfectly  fitting  bore  has 
been  made. 

Note  20.  —  Before  use,  every  piece  of  closed  apparatus  employed 
in  this  and  all  succeeding  experiments  must  be  tested  for  air- 
tightness,  and  rendered  perfectly  air-tight.  In  this  instance  place 
in  the  flask  enough  water  to  cover  the  lower  end  of  the  longer 
tube  and  transfer  the  rubber  connection  to  the  shorter  glass  tube 
and  close  it  with  a  clamp.  Now,  blow  through  the  longer  tube  so 
that  a  few  bubbles  of  air  pass  into  the  flask.  If  the  apparatus  is 
air-tight  the  water  will  rise  in  this  tube  when  the  mouth  is  with- 
drawn and  will  remain  in  an  elevated  position.  If  the  water  grad- 
ually sinks  to  its  former  level,  the  apparatus  is  not  air-tight. 
Examination  of  the  holes  in  the  cork  may  show  defects,  which  can 
be  remedied  only  by  boring  a  fresh  cork  more  carefully.  If  the 
cork  itself  contains  pores,  these  may  often  be  closed  by  thorough 
wetting.  Do  not  on  any  account  employ  paraffin  or  sealing-wax 
to  patch  defective  places  in  a  cork ;  use  a  fresh  one. 

Note  21. — Distilled  water  is  to  be  used  for  making  solutions 
and  for  rinsing  glassware  (why?).  Common  water  is  to  be  used 
for  all  other  purposes. 

6.  Use  of  the  Simple  Balance  [Instructions.  Quant.].  By 
turning  the  screw  attachment  in  front  of  balance  case,  release 
the  beam  and  pans,  allowing  the  beam  to  swing.  Observe  the 
excursions  made  by  the  pointer.  Divide  by  two  the  total  divi- 
sions covered  by  the  pointer  in  one  full  swing,  and  count  off 
from  either  end  of  the  swing  the  divisions  which  this  number 
designates,  thus  finding  the  position  of  the  true  zero  point.  The 
beam  must  swing  freely  during  the  observation :  the  zero  is  never 
to  be  read  with  the  beam  at  rest. 

This  observed  zero  point  may  lie  a  little  to  the  right  or  to  the 
left  of  the  marked  zero.  Note  down  its  distance,  in  scale  divi- 
sions, from  the  marked  zero.  If  it  lies  to  the  right,  prefix  to 
the  number  of  divisions  the  plus  (  +  )  sign;  if  to  the  left,  the 
minus  (  — )  sign.  The  zero  of  any  one  balance  changes,  and 
must  be  redetermined  every  time  a  weighing  is  made. 

Place  a  10  g.  weight  in  each  pan  [Note  22,  below],  and  deter- 
mine the  zero  as  before.  Add  the  .01  g.  weight  to  the  right- 
hand  pan,  and  find  the  reading  about  which  the  pointer  now 
oscillates.  The  difference  in  reading  between  this  point  and  the 
last  determined  zero  point  gives  the  deflection  due  to  the  .01  g. 
weight.  It  may  be  used  for  estimating  weights  less  than  .01  g. 


§7] 


MANIPULATION 


Note  22.  —  Great  care  must  be  taken  in  the  use  of  the  balance 
and  weights.  The  pans  of  the  former  must  be  let  down  upon 
their  supports  when  not  in  use  and  every  time  weights  or  other 
objects  are  to  be  added  or  removed.  All  objects  to  be  placed  upon 
the  pans  must  previously  be  carefully  cleaned  and  dried.  Solids 
are  placed  upon  a  watch-glass  or  upon  a  piece  of  glazed  paper,  and 
never  directly  upon  the  pans.  The  weights  must  be  lifted  from 
their  case  by  means  of  forceps,  never  by  the  fingers.  They  are 
usually  placed  on  the  right-hand  pan,  the  objects  to  be  weighed 
on  the  left. 

Note  23.  —  In  reckoning  results,  count  first  by  the  places  vacant 
in  the  box,  and  check  by  count- 
ing the  weights  themselves.  This 
will  enable  you  to  avoid  the  com- 
monest error  in  weighing.  Finally 
record  the  weights  in  the  note- 
book, or  laboratory  outline,  and 
never  upon  loose  sheets  of  paper, 
as  loss  of  the  latter  will  necessi- 
tate a  repetition  of  the  entire 
experiment. 

7.       Measuring     Vessels 
[Quant.]. 

a.  Fit   a  burette  (Fig.  2) 
with  a  short  piece  of  rubber 
tubing  and  glass  nozzle  (see  6). 
The  withdrawal  of  liquid  from 
the  burette  is  regulated  by  a 
pinch  clamp  upon  this  rubber 
connection,   or  by  placing  a 
small  piece  of  glass  rod  (with 
fire-polished    edges)     in    the 
middle  of  the  rubber  tubing 
to   choke  the  bore.     In  this 
latter  case,  pinching  the  tub- 
ing surrounding  the  glass  rod 
will  permit  the  liquid  to  flow 
at  any  desired  rate  from  the 
nozzle. 

b.  Support  the  burette  upon 
a   ring-stand   by  means  of  a 

clamp.      Now  fill  the  burette  Fig.  a 

with  distilled  water,  drawing 

off  a  portion  to  insure  the  complete  removal  of  air  from  the 
rubber  tubing  and  nozzle.  The  last  bubble  of  air  may  be  re- 
moved by  turning  the  nozzle  upward  while  the  water  is  allowed 


8  MANIPULATION  [§  7 

to  flow.     Read  the  height  of  water  by  observing  the  lower 
side  of  the  meniscus  and  estimate  to  tenths  of  a  division. 

Clean  and  dry  a  small  beaker  carefully  and  weigh  it  [Quant.]. 
Allow  10-20  c.c.  of  the  distilled  water  to  run  from  the  burette 
into  the  beaker,  read  the  new  level  of  the  water,  and  ascertain 
the  volume  taken  by  subtracting  the  readings.  Weigh  the 
beaker  again  and  ascertain  the  weight  of  the  water  by  subtrac- 
tion. Calculate  from  your  figures  the  weight  of  1  c.c.  of  water. 
Keep  the  beaker  and  contents  for  use  in  c. 

c.  Place   some   distilled   water  in   the   graduated   cylinder 
and  read  its  volume.     Pour  about  10  c.c.  of  this  water  into  the 
beaker  (already  partly  filled  with  water) ,  read  the  volume  of  "the 
remainder,  and  find  by  subtraction  the  volume  poured  out. 
Now  weigh  the  beaker  once  more  and  find  the  weight  of  this 
water  by  subtracting  the  previous  weight.     Calculate  the  weight 
of  1  c.c.  of  water. 

Is  measuring  volume  by  burette  or  by  cylinder  more  accurate 
(1  c.c.  of  water  at  4°  C.  weighs  1  g.),  and  why? 

d.  Measure  by  means  of  the  cylinder,  roughly,  the  volumes  of 
water  your  flasks  and  beakers  hold,  and  record  the  figures.     Fill 
the  vessels  to  a  convenient  height  for  use,  and  not  to  the  brim. 


CHAPTER  II. 


CHARACTERISTICS    OF   CHEMICAL   PHENOMENA. 

8.   Qualitative  Study  of  Chemical  Phenomena. 

a.  Rub  a  pinch  (about  0.5  g.)  of  powdered  roll  sulphur  with 
a  very  small  globule  of  mercury  (use  the  dropper)  in  a  mor- 
tar (?).  When  the  mass  has  been  intimately  ground  together 
for  about  five  or  ten  minutes  and  no  particles  of  mercury  are 
longer  observable,  place  it  in  a  dry  test-tube  and  add  about 
3  c.c.  of  carbon  disulphide  [CARE.  Keep  away  from  flames],  a 
solvent  for  the  free  sulphur.  Shake  well  (do  not  apply  heat) 
and  then  pour  off  the  clear  solution  into  the  sink  [Hood.  Note 
25,  below].  Repeat,  shaking  well  and  pouring  away  the  clear 
liquid.  Continue  this  operation  until  a  sample  of  the  decanted 
liquid  fails  to  give  any  sulphur  by  spontaneous  evaporation 
upon  a  watch-glass.  What  is  the  product  remaining  in  the  tube 
[R  657]?  By  means  of  a  few  c.c.  of  carbon  disulphide  wash  this 
product  out  upon  a  filter  paper  [Note  24,  below]  and  allow  it  to 
dry.  To  show  the  composi- 
tion of  this  substance  place 
it  in  a  small  dry  test-tube 
and  heat  strongly  over  a 
flame.  What  odor  is  noticed 
at  the  mouth  of  the  tube? 
What  product  is  found  to 
sublime  upon  the  walls  of 
the  test-tube?  Rub  the  sub- 
limate with  a  glass  rod  (?). 
What  characteristics  of  chem- 
ical change  have  you  noticed 
in  the  above  experiment? 

Note  24.  —  Cut  from  a  sheet 
of  filter  paper  a  piece  7  cm. 
(3  inches)  square.  Fold  the 
square  twice  in  directions  at 
right  angles  to  one  another,  so 
as  to  obtain  a  square  of  one- 
fourth  the  previous  area.  Cut 


Fig.  3 


off  the  loose  corners  with  scissors  so  that  a  quadrant  is  formed. 
Open  the  folded  paper  so  that  a  cone  is  produced  (Fig.  3),  and 
place  the  cone  in  a  dry  glass  funnel.  Smaller  or  larger  pieces  of 
paper  are  taken  according  to  the  amount  of  the  precipitate  or 


10 


CHEMICAL  PHENOMENA 


[§8 


of  the  liquid  to  be  filtered,  the  smallest  size  that  will  serve  the 
purpose  being  preferred.  The  funnel  must  be  chosen  so  that  the 
filter  paper,  after  being  trimmed  and  placed  in  position,  does  not 
quite  reach  the  edge,  much  less  project  above  it.  While  in  use, 
Ene  funnel  is  placed  in  a  ring  on  the  stand,  and  is  not  to  be  held 
in  the  hand. 

Note  25.  —  Pour  away  all  ill-smelling  substances,  like  carbon 
disulphide,  in  the  sink  in  the  hood  and  not  in  the  ordinary  sinks 
or  jars. 

b.  Gunpowder  is  made  from  saltpeter  (potassium  nitrate), 
roll  sulphur,  and  charcoal.  Bring  specimens  of  these  three  sub- 
stances on  watch-glasses  from  the  side-shelf,  and  examine  them 
with  respect  to  properties  which  can  be  used  for  recognition  and 
separation  [R  36,  37,  39],  such  as  appearance  and  solubility  in 
various  solvents.  Try  the  solubility  of  each  in  distilled  water 
and  in  carbon  disulphide,  using  in  the  latter  case  thoroughly 
dried  test-tubes  [Notes  25  and  26].  Do  not  judge  of  solubility 
by  the  eye,  but  filter  the  mixture  [Note  24],  catch  a  few  drops 
of  the  liquid  on  a  watch-glass,  evaporate,  and  see  whether  there 
is  any  greater  stain  on  the  glass 
than  the  pure  solvent  would  itself 
have  left.  The  taste  (?)  of  the  salt- 
peter is  a  characteristic  property. 

Now  place  about  1  g.  of  gunpowder 
in  a  large  test-tube  and  add  5-10 
c.c.  of  water.  Shake  well  (after  clos- 
ing the  test-tube  with  the  thumb), 
'warm  gently,  and  filter  [Note  24]. 
Evaporate  the  filtrate  upon  a  water 
bath  or  over  a  beaker  of  boiling 
water  (Fig.  4).  Describe  and  name 
the  residue.  Dry  (why  ?)  the  filter 
paper  and  its  black  contents  over  a 
radiator  or  in  a  drying  oven.  Shake 
the  dried  product  with  cold  carbon 
disulphide  in  a  dry  [Note  26]  test- 
tube,  filter,  and  allow  the  filtrate  to 
evaporate  [Hood]  spontaneously  (?) . 
What  remains  upon  the  paper?  Did 
any  chemical  change  occur  during  the  manufacture  of  gun- 
powder? 

Why  are  the  ingredients  of  gunpowder  pulverized  so  finely  and 
mixed  so  intimately? 

Note  26.  —  To  dry  test-tubes  or  flasks  quickly  after  recent 
washing,  warm  them  slightly  in  the  Bunsen  flame,  connect  with 


Fig.  4 


§  9. 

Dish  No.  1.     Dish  No.  2. 


Wt.  of  dish  with  lead  (silver) 

Wt.  of  dish,  empty 

Wt.  of  lead  (silver) 

Wt.  of  dish  with  lead  (silver)  chloride 

Wt.  of  dish  with  lead  (silver) 
Wt.  of  chlorine 


Wt.  of  lead  (silver) 

Wt.  of  chlorine 

Wt.  of  lead  (silver)  chloride 

No.  1.     No.  2. 
Per  cent  lead  (silver)  (z) 
Per  cent  chlorine    x' 


§9]  CHEMICAL   PHENOMENA  11 

the  air  supply  of  a  blast-lamp  a  piece  of  glass  tubing  long  enough 
to  reach  to  the  bottom  of  the  vessel,  and  allow  a  gentle  stream  of 
air  to  flow  through  the  tube  and  vessel. 

9.  Law  of  Definite  Proportions  *  [Quant.]. 

a.  Obtain  two  pieces  of  pure  lead  of  different  sizes,  about 
0.5  g.  and  0.6  g.  respectively.  Clean  and  dry  two  evaporating 
dishes,  taking  care  to  remove  any  paper  labels  which  may  be 
attached  to  them,  and  weigh  each  with  care  [Quant.,  balance]. 
Place  one  piece  of  the  lead  in  each  and  weigh  again.  The  dif- 
ference will  give  the  exact  weight  of  the  lead.  Be  careful  in 
your  notes,  and  in  handling,  to  distinguish  the  dishes  from  one 
another. 

Dilute  7  c.c.  of  concentrated  nitric  acid  [Desk]  with  14  c.c.  of 
water  in  the  graduated  cylinder  and  add  to  the  lead  in  each 
dish  10  c.c.  of  the  diluted  (1 : 2)  nitric  acid.  Cover  each  dish 
with  a  watch-glass,  convex  side  downward,  and  set  upon  the 
water  bath.  When  the  action  is  over,  and  the  lead  has  entirely 
disappeared,  rinse  the  lower  surface  of  each  watch-glass  into  the 
dish  by  means  of  a  little  water  from  the  wash-bottle.  Then  add 
to  the  contents  of  each  5  c.c.  of  pure  [Side-shelf]  dilute  hydro- 
chloric acid.  This  causes  the  precipitation  of  a  compound  of 
lead  and  chlorine  whose  weight  is  next  to  be  determined.  To 
accomplish  this,  the  water  and  other  substances  present  (ex- 
cept the  lead  chloride)  being  all  volatile,  the  mixture  is  dried 
by  evaporation  on  a  water  bath.  An  extra  Bunsen  burner 
[Storeroom]  and  two  beakers  containing  water  may  be  used  as 
baths,  as  in  Fig.  4  [Hood].  A  match  inserted  between  the  dish 
and  the  beaker  permits  escape  of  the  steam  and  prevents  the 
possible  upsetting  of  the  dish  by  the  vapor.  When  the  con- 
tents of  the  dishes  are  dry,  moisten  the  contents  of  each  with 
2  c.c.  of  pure  [Side-shelf],  concentrated  hydrochloric  acid  and 
dry  once  more.  Now  transfer  the  dishes,  one  at  a  time,  to  the 
clay  triangle  supported  on  the  ring-stand,  and  heat  the  whole 
residue  cautiously  with  a  small  Bunsen  flame.  Watch  it  nar- 
rowly and  do  not  allow  any  of  it  to  melt.  When  the  dishes  are 
cold,  weigh  each  again  with  care.  The  increase  in  weight  over 
the  previous  value  in  each  case  gives  the  weight  of  chlorine 
which  has  combined  with  the  known  weight  of  lead. 

*  Before  beginning,  always  endeavor  to  ascertain  the  object  of  each 
experiment.  By  this  means  confused  work  and  much  waste  of  time 
will  often  be  avoided,  and  significant  facts  to  be  observed  and  recorded 
will  not  escape  notice.  Consider,  first,  carefully  the  title,  as  it  will 
usually  indicate  the  object  of  the  exercise.  If  the  title  is  not  at  once 
fully  understood,  look  up  the  topic  in  a  reference  book  before  going 
further. 


12  CHEMICAL   PHENOMENA  [§  9 

Calculate  from  each  of  the  two  sets  of  data  the  percentage  of 
lead  (x)  and  of  chlorine  (x'}  in  lead  chloride  : 

Wt.  of  lead  used:  Wt.  of  lead  chloride  :  : x  :  100. 
Wt.  of  chlorine  found  :  Wt.  of  lead  chloride  :  :  x'  :  100. 
Compare  the  results  of  the  two  measurements  and  interpret. 

b.  To  secure  almost  ideal  results,  two  pieces  of  pure  silver 
foil  of  about  0.5  g.  and  0.6  g.  should  be  substituted  for  the  lead 
in  a. 

Dilute  5  c.c.  of  concentrated  nitric  acid  [Desk]  with  5  c.c.  of 
distilled  water  in  the  graduated  cylinder  and  add  to  the  silver 
in  each  dish  5  c.c.  of  the  diluted  (1 : 1)  acid.  When  the  action 
is  over,  and  the  cover-glasses  have  been  rinsed,  as  in  a,  add  2  c.c. 
of  pure  [Side-shelf]  dilute  hydrochloric  acid  to  the  contents  of 
each  dish.  This  causes  precipitation  of  a  compound  of  silver 
and  chlorine.  Evaporate  the  liquids  to  dryness  [Hood]  and 
heat  the  residues  at  once  until  signs  of  melting  are  seen. 
Weigh  each  dish.  The  increase  in  weight  over  the  previous 
value  in  each  case  gives  the  amount  of  chlorine  which  has  com- 
bined with  the  known  weight  of  silver. 

Calculate  from  each  of  the  two  sets  of  data  the  percentages 
of  silver  (x)  and  of  chlorine  (x'}  in  silver  chloride : 

WU  of  silver  used  :  Wt.  of  silver  chloride  :  :  x  :  100. 
Wt.  of  chlorine  found  :  Wt.  of  silver  chloride  :  :  x'  :  100. 

Compare  the  results  of  the  two  measurements  and  interpret. 

Before  cleaning  the  dishes,  transfer  the  silver  chloride  to  the 
bottle  for  silver  waste. 

c.  Clean  and  dry  two  evaporating  dishes,  taking  care  to 
remove  paper  labels  which  may  be  pasted  upon  them.     Weigh 
each   dish   [Quant.,   balance].     Place   in   each   some   sodium- 
hydrogen  carbonate,  in  the  one  about  1  g.  and  in  the  other  about 
2  g.,  and  weigh  again.     Treat  both  alike,  as  follows:  Dissolve 
the  solid  in  pure  dilute  hydrochloric  acid  [R  93],  adding  little 
by  little  and  covering  with  a  watch-glass  between  successive 
additions  to  avoid  loss  by  spirting.     When  the  solid  has  wholly 
dissolved,  wash  the  watch-glass  over  the  dish,  and   evaporate 
[Hood]  the  contents  of  the  latter  on  the  water  bath,  or  on  a 
beaker  of  boiling  water  (Fig.  4).     (Avoid  loss  of  time  by  bor- 
rowing a  second  Bunsen  burner  and  gas  tubing  temporarily 
from  the  storeroom.)    Allow  the  dishes  to  cool,  and  weigh.    To 
make  sure  that  the  drying  was  complete,  heat  once  more  for 


§9]  CHEMICAL  PHENOMENA  13 

half  an  hour  and  weigh  again.  This  precaution  is  taken  in  all 
experiments  of  this  kind.  The  product  is  common  salt.  Cal- 
culate the  proportion  of  carbonate  taken  to  salt  produced  thus: 

Wt.  of  carbonate  :  Wt.  of  salt  :  :  1  :x. 

Compare  the  two  values  of  x  found  from  the  two  differing  quan* 
tities  of  the  carbonate  and  interpret. 

What  physical  property  of  hydrochloric  acid  permits  use  of 
an  excess  of  the  acid  without  damage  to  the  result?  What 
form  of  statement  of  the  law  is  verified  directly  by  this  experi- 
ment? 


CHAPTER  HI. 

OXYGEN. 

10.  Sources   (p.   11,  footnote).     Heat   small   quantities  of 
barium  peroxide,  lead  dioxide,  potassium  nftrate,  silicon  dioxide 
(sand),  and  manganese  dioxide  (dry  this  before  use  by  heating 
it  for  a  few  minutes  in  a  porcelain  crucible)  separately  in  a  hard 
glass  test-tube  [Note  27].     Observe  whether  any  gas  is  given 
off,  and  apply  the  test  of  the  glowing  splinter  of  wood  [Note  28]. 
If  the  Bunsen  flame  proves  inadequate,  try  the  blast-lamp. 
Note  any  changes  in  appearance  during  the  heating  and  de- 
scribe the  residues  [Note  29].     Clean  the  test-tube  carefully 
with  hot  nitric  acid  [CARE]  and  dry  it  [Note  26,  p.  10]  after 
each  experiment. 

Note  27.  —  Use  the  clamp  and  ring-stand  to  support  the  tube, 
or  grasp  it  by  means  of  a  strip  of  folded  filter  paper 
f=t  (Fig.  5).     In  either  case  it  must  be  kept  in  a  horizontal 

gj}      position,  etherwise  condensed  moisture  may  run  down 
and  cause  it  to  crack. 

Note  28.  —  Use  a  long  splinter  of  pine  wood   [Side- 
shelf]  bearing  a  spark  at  one  end  (why  not  an  ordinary 
match?).     Such  a  splinter  is  at  once  kindled  by  oxygen. 
Note  29.  —  Beginning  with  this  chapter  include    in 
p.  your    notes    equations    for    all    the  chemical  changes 

you  observe.  When  no  change  is  observed,  do  not 
attempt  to  give  an  equation  until  otherwise  instructed 
(Chap.  IX).  In  the  present  experiments  the  formulae  of  the 
materials  used  will  have  to  be  sought  in  the  text-book.  The 
formulae  of  the  products  will  also  be  sought  in  the  book  after  the 
physical  properties  of  the  product  and  the  evolution  or  non- 
evolution  of  oxygen  have  been  noted  and  an  indication  of  what 
to  seek  for  has  thus  been  obtained.  For  other  information  in 
regard  to  the  note-book,  see  the  "General  Instructions,"  Notes 
1-5,  p.  1. 

11.  Catalytic  Action. 

a.  Place  in  a  test-tube  a  little  potassium  chlorate,  fix  the 
tube  in  a  vertical  position  by  means  of  a  burette  clamp  attached 
to  the  ring-stand,  and  melt  the  substance  at  the  lowest  tem- 
perature at  which  this  is  possible  (patience!).  Note  whether 
there  is  evidence  of  the  evolution  of  oxygen.  Now  throw  into 
the  molten  material  a  pinch  of  powdered  manganese  dioxide  (?) 
[Note  2,  p.  1],  keeping  the  face  out  of  the  path  of  anything 

14 


12] 


OXYGEN 


15 


which  may  accidentally  be  projected  from  the  tube.  Interpret 
[R  65,  75]. 

6.  Devise  a  way  of  showing  that  the  manganese  dioxide, 
used  as  in  a,  remains  unchanged  after  the  action,  and  that  it 
is  the  potassium  chlorate  that  loses  its  oxygen,  and  try  it  (?). 
Consult  the  instructor  in  regard  to  the  details  of  your  plan 
before  executing  it. 

12.  Preparation.  Mix  on  paper  about  5  g.  of  potassium 
chlorate  and  3  g.  of  powdered,  dried  (see  10)  manganese  dioxide. 
Place  the  mixture  in  a  hard  glass  test-tube  provided  with  a  one- 


Fig.  6 

hole  cork  and  delivery  tube  (Fig.  6).  Test  the  apparatus  to 
see  that  it  is  air-tight.  (In  this  instance,  place  the  end  of  the 
delivery  tube  in  the  mouth,  withdraw  some  of  the  air  by  suc- 
tion, and  note  whether  or  not  the  tongue  will  adhere  to  the 
end  of  the  tube.  If  it  will  not,  there  is  a  leakage  which  must 
be  remedied.) 

Clamp  the  test-tube  on  the  ring-stand  and  heat  carefully, 
so  as  not  to  cause  too  violent  an  evolution  of  oxygen.  Collect 
four  bottles  of  the  gas  over  water  in  a  pneumatic  trough,  taking 
care  to  remove  the  delivery  tube  from  the  water  as  soon  as  the 
bottles  are  full  of  oxygen  (why?).  The  test-tube  may  be 
cleaned  by  allowing  it  to  soak  in  water. 


16 


OXYGEN 


[§13 


13.  Properties  [Note  5,  p.  1]. 

a.  Place  a  very  small  amount  of  sulphur  in  a  deflagrating 
spoon,  ignite  it  and  then  lower  into  a  bottle  of  oxygen  (?) 
[Note  2,  p.  1]. 

Remove  the  spoon,  add  a  little  water  to  the  jar,  close  the 
mouth  with  the  hand  and  shake  (?).  Test  the  water  with  blue 
litmus  paper  or  solution  [R  70-71,  355]. 

6.  Place  a  little  red  phosphorus  in  the  spoon,  ignite  it,  and 
lower  into  the  second  bottle  (?). 

Proceed  as  in  a.     Test  with  blue  litmus  [R  70-71]. 

(If  yellow  phosphorus  is  used,  it  must  always  be  cut  under 
water  and  handled  with  forceps.  Great  care  must  be  taken 
not  to  touch  it  with  the  hand,  as  it  catches  fire  easily,  and 
causes  very  severe  burns.  Red  phosphorus  is  safer,  and  should 
be  employed  if  available.) 

c..  Lower  a  splinter  of  glowing  charcoal  into  the  third  bottle, 
holding  it  in  the  tongs  or  wrapping  the  end  of  a  piece  of  copper 
wire  round  it  (?). 

Proceed  as  in  a  (use  no  litmus),  and  cover  the  mouth  of  the 
bottle  with  a  glass  plate.  Add  some  lime-water  (calcium 
hydroxide)  and  shake  again  [R  481-482]  (?). 

14.  Slow  Oxidation  of  Metals.     Devise  a  way  of  showing 
that  air  loses  a  part  of  its  substance  (not,  e.g.,  that  the  iron 
gets  heavier,  but  that  the   air  diminishes  in  amount)  when 
moist  iron  powder  rusts,  and  try  it.     Submit  your  arrangement 
to  the  instructor  for  criticism  before  using  it. 

16.   Weight  of  a  Liter  of  Oxygen  [Quant.]  (p.  11,  footnote). 


Fig.  7 

a.  Powder  some  potassium  chlorate;  and  dry  it  on  a  watch- 
glass  on  the  radiator,  or  high  above  a  small  Bunsen  flame,  or 
in  a  drying  oven.  Construct  an  aspirator  (Fig.  7),  using  the 


§  15  a 

Wt.  of  tube  with  chlorate 

Wt.  of  tube  with  residue 

Wt.  of  oxygen 

Wt.  of  beaker  with  water 
Wt.  of  beaker 
Wt.  of  water 


Temp,  in  lab. 

Temp,  near  barometer 

Barometric  reading 

Correction 

Barometer  (corr.) 

Aqueous  tension  at  temp,  of  lab. 

Partial  press,  ox. 


§  15]  OXYGEN  17 

1-liter  bottle,  and  connect  it  with  a  hard  glass  test-tube.  Fit 
a  nozzle  to  the  rubber  tube  and  slip  a  pinch  clamp  over  the  out- 
let tube  (syphon)  in  readiness  for  closing,  at  a  later  stage,  the 
rubber  tube  that  connects  the  two  glass  tubes.  Having  inserted 
the  stopper  tightly  and  connected  the  test-tube,  test  the  appara- 
tus to  see  that  all  the  joints  are  air-tight  [Instructions:  Place 
some  water  in  the  bottle,  blow  a  few  bubbles  of  air  into  the 
apparatus  through  the  syphon,  and  observe  whether  the  water 
remains  permanently  elevated  in  the  vertical  tube.  Absolute 
certainty  that  the  apparatus  is  air-tight  must  be  reached  before 
proceeding  further]. 

Carefully  weigh  the  hard  glass  test-tube,  then  place  in  it 
between  1  g.  and  2  g.  of  potassium  chlorate  and  weigh  again. 
More  than  2  g.  is  not  needed,  less  than  1  g.  will  not  be  sufficient. 
Subtraction  gives  the  exact  weight  that  has  been  employed. 
Fill  the  bottle  almost,  but  not  quite,  to  the  shoulder  with  tap 
water.  After  reattaching  the  test-tube  make  sure  that  the 
apparatus  is  once  more  air-tight,  by  repeating  the  above- 
described  test.  Next  fill  the  syphon  and  nozzle  completely 
with  water  by  blowing  sharply  through  the  latter,  and  close  the 
clamp.  Allow  the  nozzle  to  touch  the  bottom  of  a  beaker 
(400  c.c.)  containing  some  water.  Now  open  the  clamp  and 
raise  the  beaker  till  the  levels  of  the  water  in  this  and  the  bottle 
are  the  same,  and  the  gaseous  pressure  therefore  alike  in  both. 
Close  the  clamp  again,  empty  the  beaker  and  replace  it  in 
position. 

Open  the  clamp  once  more  and  decompose  the  compound 
slowly  by  heating,  catching  in  the  beaker  the  water  driven 
over  by  the  gas.  During  the  earlier  stages  a  smoke,  consisting 
of  solid  particles,  will  arise.  This  must  on  no  account  be  driven 
into  the  connecting  tube,  as  all  the  solid  must  remain  in  the 
test-tube  to  be  weighed  (why?).  Suspend  the  heating  as  often 
as  may  be  necessary  to  let  this  smoke  settle.  During  such 
intervals  of  waiting  see  that  the  nozzle  is  constantly  immersed 
in  the  water  that  has  already  passed  over  (why?).  Stop  heat- 
ing if  the  tube  shows  signs  of  softening  [Note  30,  below]  or 
when  the  decomposition  is  complete.  For  the  purpose  of  this 
experiment  (see  15  6)  it  is  not  necessary  that  the  action  should 
be  carried  to  completion.  If,  when  the  heating  is  stopped, 
the  nozzle  is  not  under  water,  raise  the  beaker  until  it  is  well 
covered.  Allow  the  whole  apparatus  to  stand  until  it  has 
reached  the  temperature  of  the  air.  Some  water  will  return 
to  the  bottle  by  the  syphon  during  the  cooling.  Admission  of 
air  to  the  syphon  through  the  nozzle  at  any  stage  will  prevent 
this  transference,  which  is  essential  to  the  success  of  the  ex- 


18  OXYGEN  [§  15 

periment.  Equalize  the  levels  of  the  water  in  both  vessels  by 
raising  or  lowering  the  beaker,  and  then  close  the  clamp. 

Measure  the  volume  of  water  in  the  beaker  by  weighing  the 
vessel,  first  with  and  then  without  the  water,  upon  the  labo- 
ratory scales.  The  difference  in  weight  in  grams  represents 
with  sufficient  accuracy  the  number  of  c.c.  of  water  displaced 
and  hence  of  oxygen  evolved  in  the  operation  (what  of  the  air 
originally  in  the  apparatus?).  Weigh  the  test-tube  once  more 
with  care  [Balance].  Observe  at  the  same  time  the  tempera- 
ture in  the  laboratory  to  learn  the  temperature  of  the  oxygen, 
and  read  the  barometer  [Note  31,  below]  to  learn  the  pressure 
of  the  air  and  therefore  of  the  oxygen. 

Subtract  the  aqueous  tension  (Appendix  II)  at  the  observed 
laboratory  temperature  from  the  barometric  reading  (corr.) 
to  get  the  true  (partial)  pressure  of  oxygen  in  the  bottle.  Reduce 
the  volume  by  rule  to  0°  and  760  mm.  The  weight  of  this 
volume  of  oxygen  is  obtained  by  subtracting  the  weight  of  the 
residue  in  the  test-tube  from  the  weight  of  the  potassium 
chlorate  originally  taken.  Calculate  by  proportion  from  the 
data  obtained  the  weight  of  1  liter  of  oxygen  (x) : 

Vol.  of  ox.  found  :  Wt.  of  ox.  found  :  :  1000  c.c.  :  x. 

Calculate  also  the  volume  occupied  by  32  g.  of  oxygen.  To 
what  class  of  gases  would  the  use  of  the  aspirator  be  confined 
for  purposes  like  the  above? 

Note  30.  —  To  avoid  softening  of  the  glass,  through  overheating, 
watch  the  color  of  the  Bunsen  flame.  The  blue  flame  is  tinged 
with  a  yellow  color  (caused  by  compounds  of  sodium  in  the  glass) 
where  trie  flame  encounters  the  overheated  part  of  the  tube. 

Note  31. — When  the  barometer  is  read,  the  height  must  be 
"corrected"  to  that  of  a  column  of  mercury  at  0°  (Appendix  I). 

6.  Detach  the  hard  glass  test-tube  from  15  a  and  drive  off 
the  last  traces  of  oxygen  by  heating  strongly  every  portion  of 
the  tube  to  which  any  of  the  residue  adheres.  Allow  it  to  cool 
and  weigh.  Obtain  the  weight  both  of  the  residue  (potassium 
chloride)  and  of  the  total  oxygen,  by  difference. 

Assuming  the  formula  of  the  chloride  to  be  KC1,  that  of  the 
chlorate  is  KClOar.  The  formula  weight  of  KC1  being  39.15  + 
35.45  =  74.6,  find  the  formula  weight  of  O*  by  the  proportion: 

Wt.  of  KC1  found  :  Wt.  of  oxygen  found  :  :  74.6  :  y, 

where  y  =»  Oa?.  This  will  be  a  multiple  of  16  by  a  whole 
number  (why?)  if  the  measurement  has  been  carried  out  suc- 
cessfully. What  formula  do  you  find  for  potassium  chlorate? 
Write  the  equation  for  the  decomposition  of  the  chlorate. 


§  156 

Wt.  of  tube  with  chlorate 
Wt.  of  tube  empty 

Wt.  of  chlorate 

Wt.  of  tube  with  chloride 
Wt.  of  tube  empty. 

Wt.  of  chloride 


CHAPTER  IV. 

HYDROGEN. 

16.  Interaction  of  Metals  and  Acids. 

a.  Place  a  few  small  pieces  of  each  of  the  metals,  tin  (gran- 
ulated), copper  (a  nail),  iron  (filings),  zinc  (gran.),  lead  (gran.), 
aluminium  (turnings),  and  magnesium  (wire)  in  separate  test- 
tubes.     Place  in  the  measuring  cylinder  20  c.c.  of  pure  [Side- 
shelf],  concentrated  hydrochloric  acid  [R  93]  and  add  an  equal 
volume  of  water.     Add  5  c.c.  of  the  mixture  to  the  contents  of 
each  test-tube   (?).     Observe  each  case   critically  [Note  32, 
below]  and  record  the  results  [Note  29,  p.  14],  noting  the  order 
of  the  metals  in  respect  to  activity.    Notice  the  effect  of  heating, 
if  no  action  occurs  in  the  cold.     If  heating  seems  to  produce 
gas,  remember  that  it  may  be  hydrogen  chloride  (why?)  or 
steam  and  not  hydrogen.     The  presence  of  hydrogen  may  be 
inferred  from  continued  effervescence  when  heat  is  not  being 
furnished,  and  may  be  proved  by  the  slight  explosion  which 
follows  when  a  light  is  brought  to  the  mouth  of  the  tube.     But 
hydrogen  will  not  burn  when  mixed  with  much  air  or  with  other 
vaporous  substances  (why  ?).      After  the  action  has  ceased, 
filter  any  one  of  the  solutions  and  evaporate  [Hood]  it  to  dry- 
ness  on  the  sand  bath  (?). 

Can  you  give  any  grounds  for  the  belief  that  the  hydrogen 
comes  from  the  acid  and  not  from  the  metal  or  the  water? 

Which  metals,  not  used  above,  will  displace  hydrogen  from 
dilute  acids  [R  362,  and  Appendix  VII]  ?  In  what  ways,  if  at 
all,  does  the  order  of  activity  you  have  observed  differ  from 
that  accepted  by  chemists  ? 

In  making  the  equations  for  these  actions  all  that  is  needed, 
beyond  the  information  given  above  and  acquired  by  obser- 
vation, is  to  find  the  formulae  of  the  products.  These  are  not 
here  to  be  sought  by  measurement,  but  in  the  text-book  [R]. 

b.  Ascertain  the  influence  of  the  physical  state  of  the  metal 
on  its  apparent  activity  by  adding  some  zinc  dust  to  the  same 
acid  [R  111]. 

c.  Place  one  small  piece  of  pure  zinc  into  each  of  two  test- 
tubes  and  add  diluted  sulphuric  acid  [Desk]  to  both  tubes. 
If  little  or  no  action  takes  place  in  the  cold,  try  upon  one  tube 
the  effect  of  heating  (?).     Try  the  effect  of  putting  a  platinum 
wire  in  contact  with  the  zinc  in  the  second  tube  (?).     Notice 

19 


20 


HYDROGEN 


[§17 


where  the  hydrogen  appears  to  come  from,  and  explain  [R  96]. 
Withdraw  the  platinum  wire,  add  a  drop  of  cupric  sulphate 
solution,  and  shake  (?).  Is  the  solution  still  blue,  and  is  the 
zinc  still  silvery?  What  is  the  substance  upon  the  zinc  [R  361], 
and  what  effect  does  it  produce  upon  the  apparent  activity  of 
this  metal  ?  Explain. 

d.  Now  compare  (?)  the  behavior  of  concentrated  sulphuric 
acid  [Desk]  with  that  of  the  diluted  acid  used  in  16  c,  by  placing 
some  zinc   (gran.)  in  a  test-tube  and  adding  enough  of  the 
concentrated  acid  to  cover  the  metal  (why  not  more?).     After 
noticing  the  effect  in  the  cold  (?), apply  heat  (?).     What  prod- 
ucts are  formed  [Note  32]  ? 

e.  Try  the  interaction  of  acetic  acid  with  zinc  (gran.)  or  iron 
(filings).     Apply  heat,  if  necessary. 

Note  32.  —  In  observing  an  interaction  a  chemist  first  mixes  the 
substances  thoroughly  by  shaking.  If  nothing  occurs,  he  then 
heats.  If  his  eye  detects  evidence  of  the  production  of  a  gas  or 
vapor,  he  finally  smells  the  contents  of  the  tube.  Apply  these 
three  methods  of  observation  to  d  before  drawing  any  conclusion. 

17.   Other  Methods  of  Obtaining  Hydrogen. 

a.  Describe  the  result   of  throwing  pieces  of  sodium  and 
of  potassium  into  water,  as  you  recall  having  seen  it  [Class- 
room].    What    other    metals    displace    hydrogen    from    water 
[R362]? 

b.  Fit  a  test-tube  with  a  one-hole  cork  and  delivery  tube 
(Fig.  6).     Pulverize  about  2  g.  of  sodium  hydroxide,  mix  it 
intimately  in  the  mortar  with  about  3  g.  of  zinc  dust,  and  place 
the  mixture  in  the  test-tube.     Insert  the  cork  and  delivery 
tube,  test  the  apparatus  for  air-tightness  (12),  and  clamp  the 
tube  in  a  horizontal  position  (why?).     Heat  the  mixture  and 

collect  the  gas  (?)  over  water  (Fig.  6) 
in  a  test-tube.  If  the  tube  should 
crack  [CAUTION!]  cease  heating  at 
once.  To  learn  whether  the  gas  is 
combustible,  carry  the  test-tube, 
when  full  of  the  gas,  mouth  down- 
ward to  a  flame  (?). 

18.  Preparation  of  Hydrogen 
[Same  apparatus  is  used  for  19 
and  20].  Fit  a  250  c.c.  flask 
with  a  safety  tube  and  exit  tube 
(Fig.  8),  and  test  for  air-tight- 
ness. Place  in  the  flask  some 


Fig.  8 


commercial,  granulated  zinc,  close  the  apparatus,  and  attach 
to  the  b-shaped  exit  tube,  by  means  of  a  short  piece  of  rubber 


§  19]  HYDROGEN  21 

tubing,  a  longer  glass  delivery  tube.  Now  pour  30-40  c.c,  of 
dilute  hydrochloric  acid  [Desk]  through  the  safety  tube.  Test 
the  issuing  gas  until  it  is  found  free  from  air  [Instructions: 
The  gas  must  not  be  ignited  at  once  or  the  apparatus  will  be 
blown  up  (whence  comes  the  air  mixed  with  the  hydrogen?). 
Collect  samples  of  the  gas  from  time  to  time  by  raising  the 
delivery  tube  and  inserting  it  to  the  upper  part  (why?)  of  a 
test-tube  held  in  an  inverted  position,  and  then  bringing  the 
mouth  of  the  tube  (still  inverted)  to  a  distant  flame.  When 
the  gas  contained  in  the  test-tube,  after  the  first  explosion  of 
the  part  nearest  to  the  mouth,  burns  quietly,  the  gas  is  free  from 
air.  Call  an  instructor  to  inspect  the  test].  Keep  the  appara- 
tus in  operation  for  use  in  19  and  20. 
19.  Properties  of  Hydrogen. 

a.  By  collection  over  water  in  the  pneumatic  trough,  fill  a 
test-tube  with  hydrogen.     Using  this,  and  a  similar  test-tube 
filled  with  air,  show  by  an  experiment  that  hydrogen  is  lighter 
than  air  (?). 

Fill  another  test-tube  with  hydrogen  and  apply  it  closely, 
mouth  downward,  to  a  test-tube  of  air,  mouth  upward.  Allow 
the  tubes  to  remain  in  this  position  for  three  minutes,  then 
bring  first  the  lower  and  then  the  upper  tube  quickly  to  a 
flame  (?).  What  fact  about  diffusion  does  the  result  illustrate? 

b.  Fill  another  test-tube  with  hydrogen,  as  in  a,  and,  hold- 
ing it  mouth  downward,  insert  into  the  tube  a  burning  match. 
Does  the  match  continue  to  burn?    Explain. 

c.  Remove   the   glass  delivery  tube,   and   connect   a   glass 
nozzle  with  the  exit  tube  of  the  generating  flask.     Press  the 
mouth  of  the  nozzle  close  against  the  side  of  a  cold,  dry  beaker. 
If  moisture  is  deposited  (what  is  its  source?),  fill  a  U-tube  with 
calcium  chloride  [R  100]  and  connect  it  between  the  exit  tube 
and  the  nozzle.     Does  the  gas  now  deposit  moisture  upon  a 
beaker?      If  not,  ascertain  that  the  issuing  gas  is  not  explosive 
(see  test  in  18),  and  set  fire  to  it.     What  is  the  color  of  the 
flame?     Does  the  color  change,  and,  if  so,  why?    Hold  a  cold, 
dry,  inverted  beaker  over  the  flame.     What  is  deposited  on  the 
beaker?    Why  did  we  use  dried  hydrogen  for  this  experiment? 
Keep  the  apparatus  in  operation  for  20,  unless  a  Kipp's  appa- 
ratus is  available  or  hydrogen  is  furnished  in  the  laboratory. 

Remove  the  nozzle  with  its  rubber  connection  and  push  the 
latter  tightly  into  the  end  of  the  gas  tubing  furnished  with  the 
Bunsen  burner.  Connect  the  other  end  of  the  tubing  with 
the  illuminating-gas  supply.  Turn  on  a  gentle  stream  of  gas  and 
set  fire  to  it.  Hold  a  cold,  dry  beaker  over  this  flame  (?). 
What  inference  in  regard  to  illuininating-gas  do  you  draw? 


22  HYDROGEN  [§  20 


J 


20.  Reduction  by  Means  of  Hydrogen  [Two  students  work- 
ing together].  Fit  a  hard  glass  tube,  25-30  cm.  long  and  open 
at  both  ends,  with  perforated  corks  and  short  glass  tubes  (Fig. 
9).  Support  it  on  the  ring-stand  by  means  of  a  clamp  grasping 

it  close  to  one  end.  Dry  1-2  g. 
of  ferric  oxide  by  heating  in  a 
porcelain  crucible.  Put  the  oxide 
into  the  porcelain  boat  and  place 
-..-.- .M  *•'!=*  the  latter  in  the  hard  glass  tube 
near  the  end  remote  from  the 
clamp  (why?),  but  not  so  near 
that  the  subsequent  heating  will 
char  the  cork.  Insert  the  corks 
with  their  tubes.  Connect  the 

: .      tube   nearest  to  the   boat  with 

I — u — \  a  Kipp's  apparatus  and  drying 

/         \  bottle    (Fig.    18)    delivering  dry 

Fig.  p  hydrogen,    or   with   the  labora- 

tory supply  of  the  gas,  or  with 
the  apparatus  furnishing  dry  hydrogen  used  in  18. 

Test  the  issuing  gas  to  see  that  it  is  not  explosive  (see  18) 
and  repeat  the  test  every  time  the  apparatus  is  opened.  Now 
heat  the  boat  and  contents,  at  first  gently  by  waving  the  flame 
under  the  tube,  and  later  strongly  until  the  material  is  red-hot 
(what  temperature  is  used  [R  73]  ?).  Observe  the  effect  upon 
the  ferric  oxide  [R  756]  (?).  Does  anything  condense  in  the 
cooler  end  of  the  tube? 

What  is  the  action  of  steam  upon  heated  iron  [R  98]  ?  How 
do  you  reconcile  this  fact  with  that  observed  above? 

Repeat  the  above  experiment,  using  freshly  heated  alumin- 
ium oxide  in  place  of,  ferric  oxide,  and  otherwise  following  the 
directions  exactly  (?).  If  no  effect  is  noticed  after  an  oxide 
has  been  at  a  red  heat  for  three  minutes,  absence  of  action 
may  be  inferred.  How  do  you  account  for  the  result  obtained 
with  aluminium  oxide?  Which  oxides  are  reducible  by  hydro- 
gen [R  362]  ? 

WTiat  are  the  commercial  and  mineralogical  names  given  to 
the  two  oxides  used  in  these  experiments  [R]  ? 


CHAPTER  V. 

WATER   AND   SOLUTION. 

21.  Purity  of  Water.     Place  a  few  drops  of  distilled  water 
on  a  clean  watch-glass  (not  an  evaporating-dish.     Why?)  and 
evaporate  on  the  water  bath.     Do  the  same  with  ordinary  water. 
Observe  whether  any  stains  remain  on  the  glasses  (?).     What 
class  of  impurities  would  leave  no  trace  of  their  presence  in 
this  test? 

22.  Union  with  Oxides.     Place  a  pinch  of  cupric  oxide  in  a 
test-tube  and  wash  it  by  shaking  with  a  little  distilled  water 
and  pouring  off  the  liquid.     Add  more  water  and  shake  again. 
Test  this  latter  solution  with  litmus  paper  (?).     At  the  same 
time    test    a    sample    of   the   water  with   litmus    paper   and 
compare  the  tints.     Repeat  with  barium  oxide  (?). 

Recall  the  behavior  of  acid-forming  oxides  examined  in  13. 
Some  oxides  do  not  interact  readily  with  water  (which?).  These 
oxides  which  do  interact  may  be  divided,  according  to  the 
natures  of  the  products  they  give,  into  two  classes.  What  are 
those  classes,  and  which  oxides  belong  to  each?  What  are  the 
two  classes  of  elements  whose  oxides  belong  to  the  two  groups, 
respectively  [R  119]? 

23.  Hydrates. 

a.  Heat   some    blue   vitriol    (p.    4,   footnote)    gently  in    a 
porcelain   crucible    (?).     Allow   a   very   small   portion   of   the 
white  powder  to  stand  exposed  to  the  air  on  a  watch-glass  (?). 
Dissolve  the  remainder  by  boiling  with  the  minimum  amount  of 
water  required  to  dissolve  it,  and  set  the  solution  aside (?).  What 
chemical  actions  have  taken  place  in  these  three  operations  ? 

b.  [Quant.]     Place  small  quantities  (about  1  g.)  of  Glauber's 
salt  and  of  blue  vitriol  in  two  porcelain  dishes  and  ascertain 
the  gross  weight  in  each  case.     Allow  the  dishes  and  contents 
to  remain  for  24  hours  or  more  and  weigh  again  (?).     Interpret 
the  results  [R  121]. 

c.  Gently  warm  small  quantities  of  barium  chloride,  potas- 
sium nitrate,  magnesium  sulphate,  and  potassium  dichromate 
separately  in  dry  test-tubes  and  notice  whether  they  undergo 
any  change  [R]. 

Are  all  crystalline  substances  hydrates?  Classify  the  sub- 
stances you  have  examined  into  two  groups  with  reference  to 
this  property. 

23 


24  WATER  AND  SOLUTION  [§  24 

d.  Take  in  a  test-tube  about  5  c.c.  of  commercial,  concen- 
trated sulphuric  acid,  place  in  it  a  crystal  of  blue  vitriol  and 
let  the  materials  stand  for  an  hour,  or  more  (?)  [R  388].     Now 
heat  the  contents  of  the  tube  to  the  boiling-point  of  the  acid, 
holding  the  test-tube  in  a  test-tube  holder,  keeping  it  far  from 
the  clothing,  and  taking  care  that  none  of  the  contents  spirt 
out  upon  the  hands  or  face  [CAUTION:  Sulphuric  acid  burns 
are  very  painful.     Note  16,  p.  2].     After  the  contents  of  the 
tube  have  settled,  pour  off  the  clear  liquid  into  another  tube. 
On  the  following  day,  examine  the  little,  shining  particles  on 
the  sides  of  the  tube.     What  is  their  color,  and  condition?    Of 
what  are  they  composed  [R  625]  ? 

Are  the  compounds  (such  as  cupric  sulphate)  which,  in  pres- 
ence of  water,  yield  crystalline  hydrates,  amorphous  or  crys- 
talline in  its  absence?  What  is  the  true  significance  of  the 
crystalline  condition  [R  123]  ? 

e.  Take  a  clean  match-stick  and,  after  dipping  it  in  a  solu- 
tion of  cobalt  chloride,  write  upon  a  piece  of  white  paper.   After 
the  writing  is  dry,  warm  the  paper  gently  by  waving  it  above 
a  Bunsen  flame  (?).     Now,  breathe  repeatedly  upon  the  writ- 
ing (?).     Write  equations  for  the  actions  that  have  occurred 
[R  759]. 

/.  [Quant.]  Put  about  1  g.  of  crystals  of  gypsum  in  a  weighed 
porcelain  crucible  and  weigh  again.  Place  the  crucible  on  the 
clay  triangle,  heat  to  redness  until  no  further  loss  in  weight 
occurs,  and  determine  by  difference  the  loss  in  weight  (water) 
and  the  weight  of  the  calcium  sulphate  remaining. 

The  formula  of  gypsum  must  be  CaSO4,:rH2O.  Assuming 
the  formula- weights  of  calcium  sulphate  (CaS04  =  136)  and 
of  water  (H2O  =  18)  calculate  from  your  data  the  value  of  x. 

Wt.  of  calcium  sulphate:  Wt.  of  water  :  :  136  :  xx  18. 

What  is  the  formula  of  gypsum? 

24.  Solution:  Gases  in 
Liquids.  Half  fill  a  1-liter 
bottle  with  distilled  water, 
cork,  and  shake  vigorously 
till  the  water  is  saturated 
with  air.  Take  the  tempera- 
ture of  the  water  and  also 
the  barometric  reading.  Fit 
F>g-  I0  a  small  flask  (100  c.c.)  with 

a  one-hole  cork  and  delivery  tube  (Fig.  10)  and  measure  its 
content  up  to  the  lower  surface  of  the  cork.  Completely  fill 
the  whole  apparatus,  including  the  delivery  tube,  with  the 


§  26]  WATER  AND    SOLUTION  25 

prepared  water,  and  boil,  collecting  the  gas  in  a  small  test- 
tube  inverted  over  water.  When  no  more  gas  comes  over, 
equalize  the  levels  of  the  water  in  the  tube  and  trough  (or 
beaker)  and  mark  the  level  in  the  tube  with  a  thin  rubber  ring 
(cut  this  from  a  piece  of  rubber  tubing).  Measure  the  volume 
which  the  air  occupied.  Correct  the  volume  for  the  aqueous 
vapor  present  only,  obtaining  thus  the  volume  of  the  air  when 
dry  and  at  the  observed  temperature  and  pressure.  Calculate 
the  volume  of  air  dissolved  by  100  c.c.  of  water  at  the  observed 
temperature  and  pressure  (?).  What  proportion  of  its  own 
volume  of  air  has  the  water  dissolved? 
26.  Solution:  Liquids  in  Liquids. 

a.  Take  5  c.c.  of  carbon  disulphide  in  a  dry  test-tube  [Note 
26,  p.  10],  and  add  to  it  5  c.c.  of  water,  a  drop  at  a  time,  shak- 
ing vigorously  after  each  addition  and  observing  whether  at  each 
stage  the  mixture  is  homogeneous  or  not  (?). 

b.  Repeat,  using  5  c.c.  of  ether  with  water  (?). 

c.  Mark  off  on  a  narrow  test-tube  by  means  of  the  trian- 
gular file  the  points  at  which  10  c.c.  and  20  c.c.  of  water  stand, 
respectively.     Empty  the    test-tube    and    pour    in    10  c.c.  of 
water,  and  then  take  10  c.c.  of  alcohol  in  the  graduated  cylinder 
and  add  it  to  the  water,  a  drop  or  two  at  a  time,  shaking  vig- 
orously after  each  addition  and  observing  as  before.     Finally, 
compare  the  volume  of  the  mixture  with  that  of  the  components 
separately  (?). 

26.   Solution:  Solids  in  Liquids. 

a.  Select  two  large  crystals  of  some  soluble,  colored  com- 
pound, such  as  blue  vitriol  (or  potassium  dichromate).     Choose 
crystals  of  approximately  equal  size  and  so  large  as  to  be  just 
capable  of  being  slipped  into  a  test-tube.     Reduce  one  of  the 
crystals  to  a  fine,  uniform  powder  in  the  mortar.     Note  and 
account  for  the  change  in  tint  (?).     Now  place  the  crystal  and 
the  powder  in  separate  test-tubes,  and  provide  two  corks  which 
fit  the  mouths  of  the  tubes.     Add  20  c.c.  of  water    simulta- 
neously to  each   tube,  and   insert  the  corks.     Read  the  time 
on  a  watch  and  shake  the  tubes  simultaneously  with  vigor, 
noting  the  time  at  which  the  solid  finally  disappears  in  each 
tube  (?).    Account  for  the  difference. 

b.  Reduce  to  a  fine  powder  10-15  g.  of  potassium  dichromate, 
using  the  larger  amount  in  warm  weather,  the  smaller  in  cool. 
Prepare  a  saturated  solution  of  the  substance  by  placing  it  in 
a  flask  with  50  c.c.  of   water  and   shaking  at  intervals  for  ten 
minutes.     So  much  of  the  solid  must  be  taken  that  an  undis- 
solved  residue  remains. 


26  WATER   AND  SOLUTION  [§26 

Take  the  final  temperature  of  the  solution.  Now  pour  the 
clear  solution  into  a  burette  attached  to  the  ring-stand,  filling 
the  apparatus  completely  to  the  point  of  the  nozzle  with  the 
liquid  (7  6).  Read  the  level  of  the  lower  side  of  the  meniscus. 
Weigh  [Quant.]  a  clean,  dry  evaporating-dish,  run  into  it  about 
22-24  c.c.  of  the  solution,  and  weigh  [Quant.]  the  dish  and  con- 
tents. Read  also  the  level  of  the  meniscus  and  note  the  volume 
of  solution  used.  Now  evaporate  the  weighed  portion  of  the 
solution  completely  to  dryness  upon  a  water  bath,  or  on  a 
beaker  of  boiling  water,  and  weigh  again.  Determine  by  dif- 
ference the  weights  of  the  dry  dichromate  here  found,  and  of  the 
water  in  which  it  was  dissolved.  Calculate  from  the  data  the 
weight  of  dichromate  which  would  be  dissolved  by  100  c.c.  of 
water  at  the  observed  temperature. 

From  the  volume  of  the  part  of  the  solution  evaporated,  and 
the  weight  of  dichromate  found  in  it,  calculate  also  the  molar 
solubility  [R  149]  of  potassium  dichromate  at  the  observed 
temperature.  Compare  the  results  with  those  which  would  be 
obtained  with  potassium  chromate  K2Cr04  (Appendix  IV)  (?). 

c.  Take  about  6  g.  of  the  dichromate  and  boil  with  10  c.c. 
of  water  in  a  test-tube.     Is  the  solubility  at  this  temperature 
different?    Allow  the  clear  solution  to  cool  (?).     Explain  the 
result.     What  sort  of  curve  of  solubility  would  this  substance 
exhibit  (Appendix  V)  ? 

Take  about  6  g.  of  sodium  chloride  and  boil  with  10  c.c.  of 
water  in  a  test-tube.  Pour  the  clear  liquid  immediately  into 
another  test-tube.  Examine  this  when  cool  (?).  Is  salt  much 
less  soluble  in  cold  than  in  boiling  water?  How  would  its  curve 
of  solubility  differ  from  that  of  potassium  dichromate? 

d.  Shake  some  powdered  calcium  sulphate  with  cold,  recently 
boiled,  distilled  water.     Ascertain  whether  any  of  the  salt  has 
gone  into  solution  (21).     Repeat  with  chalk  (calcium  carbo- 
nate), rejecting  the  water  with  which  it  is  first  shaken   (?). 
Which  of  these  substances  do  you  find  to  be  more  soluble? 
What  are  the  amounts  of  these  salts  dissolved  by  100  c.c.  of 
water  at   18°  [R  Appendix  IV]  ?      In  what  ratio  is  calcium 
sulphate  more  soluble  than  calcium  carbonate  [R  Appendix  IV]? 
In  what  ratio  is  calcium  chloride  more  soluble  than  calcium 
sulphate  [R]  ?    Which  of  all  these  substances  are  spoken  of  as 
"insoluble"? 

e.  Take  about  10  c.c.  of  water  in  a  test-tube,  add  to  it  not 
more  than  1  c.c.  of  lead  nitrate  solution,  and  mix.     Now  add 
about  2  c.c.  of  dilute  hydrochloric  acid  (?).     Repeat,  heating 
the  mixture  to  the  boiling-point  before  adding  the  hydrochloric 
acid  (?).     Examine  this  tube  again,  after  the  contents  have 


§27]  WATER  AND  SOLUTION  27 

cooled  (?).  Interpret  the  result.  Is  lead  chloride  an  "insol- 
uble" substance  [R  Appendix  IV]? 

/.  Take  about  10  c.c.  of  water  in  each  of  two  test-tubes. 
To  one  portion  add  Glauber's  salt,  previously  pulverized  in  a 
mortar,  until,  after  shaking,  a  considerable  excess  remains  un- 
dissolved.  Saturate  the  other  portion  with  anhydrous  sodium 
sulphate  in  the  same  manner.  Perform  the  last  operation 
rapidly,  taking  care  not  to  introduce  any  particles  of  the  hydrate, 
and  do  not  let  the  solution  stand  before  use.  Now  decant  the 
two  liquids  into  clean  test-tubes,  disregarding  the  cloudiness 
of  one  of  them.  Then  add  a  little  of  the  anhydrous  substance 
to  the  solution  first  made  and  a  small  crystal  of  Glauber's 
salt  to  the  contents  of  the  second  test-tube  and  shake  both  (?). 
After  a  short  time,  examine  the  contents  of  each  again  (?). 
Interpret  the  results  [R  160-161]. 

g.  Two  immiscible  solvents.  Place  one  small  particle  of 
iodine  in  each  of  three  test-tubes  and  add  to  one  water,  to  the 
second  potassium  iodide  solution,  to  the  third  carbon  disul- 
phide,  and  shake  each  (?).  If  any  iodine  remains  undissolved, 
pour  off  that  solution  into  a  clean  test-tube.  Now  add  a  drop 
or  two  of  carbon  disulphide  to  the  first  two  solutions,  shake  again 
(?),  and  describe  carefully  what  seems  to  have  happened.  Deduce 
from  this  the  relative  solubility  of  iodine  in  the  three  solvents. 

27.  Properties  of  Solutions:  Vapor  pressure  and  Boiling- 
Point. 

a.  Place  some  dry  potassium   carbonate   (or  pulverized  cal- 
cium chloride)  in  a  small  beaker  or  crucible.     Set  the  vessel  in 
an  evaporating  dish  containing  water,   and  invert  over  it  a 
larger  beaker  so  that  the  edge  of  the  latter  is  under  the  liquid. 
Examine  the  material  from  day  to  day  (?).    Remembering  that 
there  is  moisture  upon  the  surface  of  even  "dry"  bodies,  and 
that  therefore  a  solution  of  potassium  carbonate  was  present 
with  the  solid,  explain  the  change  [R  162].     To  what  class  of 
substances  do  those  which  deliquesce  all  belong?     Is  deliques- 
cence a  physical  or  a  chemical  phenomenon? 

b.  Fix  a  test-tube  containing  about   10  c.c.   of  water  hi  a 
clamp  upon  the  ring-stand.     Suspend  the  thermometer  from  a 
ring  by  means  of  a  thread,  hi  such  a  way  that  the  bulb  is  im- 
mersed in  the  water.    Boil  the  water,  using  a  small  Bunsen  flame, 
and  read  the  temperature  (?).     Now  add  to  the  boiling  water 
about  2-3  g.  of  dry  calcium  chloride,  and,  after  solution  is  com- 
plete, read  the  temperature  of  boiling  again  (?).     Add  another, 
equal  portion  of  calcium  chloride  and  repeat  the  temperature 
reading  after  the  whole  has  dissolved  (?).     Explain  [R  162]. 

c.  If  pulverized  ice  were  to  be  added  to  water  until  the 


28  WATER  AND  SOLUTION  [§  28 

solid  no  longer  melted,  what  would  be  the  temperature  of  the 
mixture?  If  ice  were  to  be  added  to  the  aqueous  solution  of 
some  substance,  until  the  ice  no  longer  melted,  how  would  the 
temperature  differ  from  that  of  water  and  ice?  Why  does  this 
difference  exist  [R  163]  ?  Why  does  salt  thrown  upon  ice  cause 
the  latter  to  melt  [R  164]  ? 

28.  Properties  of  Solutions:  Volume  Changes  and  Thermal 
Effects. 

a.  Recall  the  change  in  volume  observed  in  25  c  when  alcohol 
and  water  were  mixed  (?). 

b.  [Quant.].     Take  about  25  g.  of  potassium  carbonate  and 
determine  its  weight  to  the  nearest  tenth  of  a  gram.     Assum- 
ing the  specific  gravity  of  this  substance  to  be  2,  calculate  the 
volume  of  the  amount  you   have   taken   (?).     Place   in   the 
graduated  cylinder  exactly  85  c.c.  of  water  and  take  its  tem- 
perature.    What  is  the  sum  of  the  volumes  of  the  water  and  the 
carbonate,  separately?    Add  the  weighed  specimen  of  potas- 
sium carbonate  to  the  water,  dissolve  by  repeated  inversion 
of  the  cylinder,  closing  the  mouth  of  the  latter  with  the  hand, 
and  read  the  volume  of  the  solution  (?).     Read  also  the  tem- 
perature of  the  solution  immediately.     Is  there  a  change  in 
volume,  or  in  temperature,  on  dissolving  two  substances  in  one 
another? 

What  relation  exists  between  the  sign  of  the  thermal  effect 
when  a  substance  is  dissolved  in  a  nearly  saturated  solution  of 
the  same  substance,  and  the  change  of  solubility  with  tem- 
perature [R  260]  ?  What  do  you  infer  in  this  case? 

c.  Examine  the  solubility  curve  of  anhydrous  sodium  sul- 
phate [R  158]   (?).     Will  this  compound  give  out  or  absorb 
heat  in  dissolving  in  water  [R  260]  ?    Verify  your  conclusion  by 
trying  the  experiment  (?). 

d.  Repeat  b,  using  about  25  g.  of  ammonium  chloride  (sp. 
gr.  1.5).     Make  the  same  observations  and  answer  the  same 
questions. 


CHAPTER  VI. 


CHLORINE  AND  HYDROGEN  CHLORIDE. 


29.  Preparation  of  Chlorine  [Hood]. 

Experiments  29  b  and  30  must  be  accomplished  at  ojje  ex- 
ercise. 29  a  may  be  postponed  to  facilitate  this. 

a.  Prepare  some  strips  of  filter  paper  by  dipping  them  in 
starch  emulsion  [Side-shelf]  to  ^ich  you  have  added  one  drop 
of  potassium  iodide  solution. 

Place  small  quantities  of  finely  powdered  manganese  dioxide, 
potassium  chlorate,  lead  dioxide,  and  pure  litharge  in  as  many 
test-tubes,  and  add  a  little  commercial,  concentrated  hydro- 
chloric acid  [Desk]  to  each.  Notice  the  color  (?)  and  odor  (?) 
of  the  gas  in  each  case.  If  no  action  takes  place  in  the  cold, 
apply  heat.  Dip  into  the  gas  in  one  of  the  test-tubes  a  strip 
of  the  prepared  paper  (?).  How  do  you  account  for  the  differ- 
ence in  the  behavior  of  the  two  oxides  of  lead?  Do  all  com- 
pounds containing  oxygen  give  free  chlorine  in  this  way?  If 
not,  state  what  is  common  to  those  which  do. 

6.  Fit  up  a  250  c.c.  generating  flask,  as  in  Fig.  11  with  a 
dropping-funnel  (or  substitute  3(5  fr) 
and  an  L-shaped  glass  tube  at- 
tached to  the  exit  tube.  Use  the 
shortest  possible  rubber  connec- 
tions here  and  in  31  (hydrogen 
chloride),  as  rubber  tubing  is 
destroyed  by  these  gases.  Test 
the  apparatus  to  see  that  it  is  air- 
tight. Place  in  the  flask  about 
20  g.  of  dry  potassium  permanga- 
nate, and  fill  the  globe  of  the 
dropping-funnel  with  diluted, 
commercial,  concentrated  hydro- 
chloric acid  (1  Aq.  :  3  acid).  Allow  the  delivery  tube  to  dip 
to  the  bottom  of  a  small  beaker  containing  a  little  sodium 
hydroxide  solution  [Desk].  Now  admit  the  acid  drop  by  drop, 
regulating  the  flow  so  that  too  rapid  a  stream  of  gas  is  not 
produced.  The  complete  displacement  of  the  air  in  the  flask 
will  be  recognized  by  the  color  of  the  contents  and  the  fact  that 
the  bubbles  of  pure  chlorine  are  completely  absorbed  by  the 
sodium  hydroxide. 

29 


Fig.  ii 


30  CHLORINE  [§  31 

When  the  air  hag  all  been  displaced,  fill  three  dry  bottles  and 
one  dry  test-tube  with  the  gas  by  downward  displacement, 
observing  the  following  precautions:  Provide  a  piece  of  stiff 
paper  or  card,  perforated  with  a  hole  for  the  reception  of  the 
delivery  tube,  to  cover  the  bottles  during  the  filling,  and  cover 
the  vessels  with  glass  plates  as  soon  as  they  are  full.  See  that 
the  delivery  tube  reaches  to  the  bottom  (why?)  of  each  vessel 
during  the  filling.  Replace  the  end  of  the  delivery  tube  in  the 
sodium  hydroxide  when  all  the  vessels  have  been  filled.  When 
the  experiment  is  over,  pour  the  contents  of  the  generating 
flask  into  the  sink  in  the  hood,  and  not  into  one  of  the  sinks  in 
the  open  laboratory,  and  wash  down  with  much  water. 

30.  Properties  of  Chlorine  [Hood]. 

o.  In  one  bottle  of  the  gas  scatter  a  pinch  of  finely  pow- 
dered antimony  [R  715]  (?). 

6.  Take  a  clean  piece  of  sodium  [From  Instructor]  and  cut 
from  it  a  very  thin  slice  not  more  than  one-half  inch  square 
(fingers  and  knife  used  in  handling  sodium  must  be  dry!).  In- 
troduce this  piece  into  a  bottle  of  chlorine  (?)  and  cover  at  once 
with  a  glass  plate.  Examine  after  half  an  hour.  If  any  of  the 
metal  remains  unattacked,  scrape  off  the  white  deposit  and 
place  it  upon  a  watch-glass,  and  throw  the  sodium  into  the 
sink  in  the  hood.  Add  the  material  on  the  watch-glass  to 
that  in  the  bottle  and  dissolve  in  2  c.c.  of  water.  Allow  the 
solution  to  stand  in  a  watch-glass  until  it  dries,  and  examine 
the  crystals  with  a  lens  (?). 

c.  Connect  a  glass  nozzle  with  the  illuminating-gas  supply, 
and  lower  a  small,  burning  gas-jet  into  the  third  bottle  (?). 
Blow  the  breath  into  the  bottle  after  withdrawing  the  jet  (?). 

d.  Fill  a  test-tube  with  hydrogen  from  a  Kipp's  apparatus 
or  from  the  laboratory  supply.      Bring  this  tube  mouth  to 
mouth  with  a  tube  of  chlorine  and  mix  the  gases  by  repeated 
inversion.     (Take  care  not  to  expose  the  mixture  to  direct  sun- 
light.)    Hold  the  mouth  of  each  tube  to  the  Bunsen  flame  (?). 
Close  the  mouth  of  one  tube  quickly  with  the  thumb,  add  a 
few  drops  of  water,  shake,  and  test  the  solution  with  litmus 
paper  (?). 

31.  Preparation  of  Hydrogen  Chloride. 

a.  [Hood]  Place  small  quantities  of  ammonium  chloride, 
barium  chloride,  mercuric  chloride,  and  sodium  chloride  in  as 
many  test-tubes,  and  add  a  few  drops  of  concentrated  sulphuric 
acid  [Desk]  to  each  (?).  Describe  what  happens  in  each  case. 
Blow  moist  air  across  the  mouth  of  the  test-tube  (?).  Lower  a 
glass  rod  dipped  in  ammonium  hydroxide  solution  into  each 
[Note  33,  below].  Try  the  effect  of  heating.  Remember  that 


§  32]  CHLORINE  31 

the  solubility  (physical)  of  the  substance  in  sulphuric  acid  will 
largely  determine  the  speed  of  the  action.  In  case  of  difficulty, 
therefore,  take  a  fresh  sample  of  the  solid,  pulverize  it  finely, 
and  shake  with  the  acid  for  some  minutes  before  heating  and 
testing.  Arrange  the  substances  in  the  order  of  apparent 
activity. 

6.  To  a  pinch  of  finely  powdered  sodium  chloride  add  a 
strong  solution  of  phosphoric  acid  and  heat  if  necessary  [R  179] 
(?).  Test  with  ammonia  as  before.  The  above  remark  about 
-olubility  applies  also  to  this  case. 

Why  is  hydrogen  chloride  displaced  completely  in  a  and  b 
by  these  acids  under  these  conditions  [R  180]? 

c.  [Hood]  In  a  250  c.c.  flask  (Fig.  11),  fitted  with  dropping- 
funnel  (or  substitute,  36  6)  and  L-shaped  delivery  tube,  place 
about  30  g.  of  common  salt.  Admit  concentrated  sulphuric 
acid  through  the  funnel.  Collect  the  gas  in  three  dry  bottles 
by  downward  displacement  (using  a  perforated  square  of  paper 
or  card  as  in  the  case  of  chlorine),  cover,  when  filled,  with  glass 
plates  and  reserve  for  32.  Place  about  10  c.c.  of  distilled 
water  in  a  test-tube,  attach  a  nozzle  to  the  delivery  tube,  and 
allow  the  gas  to  bubble  into  this  for  a  few  minutes  (?).  Re- 
serve the  aqueous  solution  also  for  32.  Write  equations  for  the 
two  possible  interactions  of  salt  and  sulphuric  acid.  Which  of 
the  two  takes  place  under  the  above  conditions? 

Note  33.  —  The  use  of  ammonia  is  not  a  specific  test  for  hydro- 
gen chloride.  It  can  be  used  only  for  ascertaining  the  presence  or 
absence  of  any  one  of  several  gases,  usually  of  acidic  character, 
which  are  capable  of  uniting  with  ammonia. 

In  writing  the  equation  here,  and  whenever  the  same  test  is 
used,  consider  whether  the  interaction  took  place  with  the  liquid 
on  the  rod  (containing  NH4OH),  or  with  the  gas  (NHJ  given  off  by 
this  liquid.  Note  the  odor  of  this  gas  (?). 

32.  Properties  of  Hydrogen  Chloride  and  of  Hydrochloric 
Acid. 

a.  Invert  one  of  the  bottles  of  the  gas  in  a  dish  of  water  (?). 
Relate  this  property  to  that  observed  on  blowing  moist  air 
into  the  gas  (31  a).  If  any  gas  remains,  what  should  you 
expect  it  to  be?  Test  your  conclusion  experimentally. 

6.  Pour  a  little  ammonium  hydroxide  solution  on  a  strip  of 
filter  paper  and  plunge  this  into  the  second  bottle  (?)  [Note 
33,  above].  Describe  the  difference  between  these  fumes  and 
those  formed  by  the  action  of  moist  air  upon  the  gas  (31  a) . 

c.  Devise  a  way  of  proving,  in  a  rough  way,  that  the  gas  is 
heavier  than  air,  and  use  the  third  bottle  of  gas  for  carrying  it 
out. 


32  HYDROGEN    CHLORIDE  [§  33 

Perform  the  following  experiments  with  the  aqueous  solu- 
tion prepared  in  31  c. 

d.  Test  the  solution  with  litmus  paper. 

e.  To  a  part  add  a  granule  of  zinc  (?). 

/.   To  a  part  add  a  crystal  of  sodium  carbonate  [R  480]  (?). 

g.  Dilute  the  remaining  portion  of  the  acid  solution  with  an 
equal  volume  of  water  and  distribute  it  between  three  test- 
tubes.  To  one  test-tube  add  a  drop  or  two  of  mercurous  nitrate 
solution  (?),  to  the  second  a  drop  of  lead  nitrate  solution  (?),  and 
to  the  third  a  drop  of  silver  nitrate  solution  (?).  After  allowing 
the  contents  of  each  tube  to  settle,  pour  away  the  liquid,  add 
water,  and  boil  (?).  Allow  to  cool,  and  note,  by  the  appearance 
of  crystals,  which  of  the  precipitates  is  soluble  in  hot  water. 

These  precipitates  are  given,  not  only  by  hydrochloric  acid, 
but  by  any  chloride,  and  are,  therefore,  means  of  recognizing 
the  presence  of  the  chloride  radical  which  is  common  to  all 
chlorides. 

33.  Theory  of  the  Method  Used  in  Preparing  Hydrogen 
Chloride.  To  a  concentrated  solution  of  sodium-hydrogen 
sulphate  add  pure  concentrated  hydrochloric  acid  (?).  Add 
the  acid  a  very  little  at  a  time  to  avoid  over-rapid  precipita- 
tion, and  agitate  between  additions.  The  longer  the  operation 
takes,  the  better.  Examine  the  result  with  a  lens  (?). 

Write  the  equation  for  this  action.  What  relation  does  this 
action  bear  to  that  in  31  c?  What  circumstances  determine 
the  direction  of  a  reversible  action  [R  180]? 


CHAPTER  VII. 

EQUIVALENT  WEIGHTS,   FORMULA,   EQUATIONS. 

34.  Composition  of  Carbon  Dioxide  [Quant.  Two  students 
working  together].  Fit  a  piece  of  hard  glass  tubing,  25-30  cm. 
long,  with  perforated  corks.  Insert  at  one  end  a  short  piece 
of  glass  tubing  and  at  the  other  a  U-tube,  as  in  Fig.  12.  The 


Fig.  12 


inner  edges  of  the  hard  glass  tube  should  be  rounded  with  a 
file,  or  flared  by  use  of  the  blast-lamp  and  a  piece  of  charcoal. 
Rubber  stoppers  will  give  tight  joints  more  surely  than  corks. 
Attach  to  the  U-tube  by  means  of  a  cork  a  short,  straight  tube, 
of  the  diameter  of  a  narrow  test-tube,  which  has  been  drawn 
out  [Bunsen  flame]  so  as  to  leave  a  small  opening  at  the  free 
end.  Arrange  a  loop  of  thread  [Side-shelf]  with  which  to  sus- 
pend the  U-tube  from  the  balance.  Place  in  the  hard  glass 
tube  a  plug  of  granular  cupric  oxide,  about  4  cm.  in  length. 
This  may  be  held  in  position  by  small  wads  of  asbestos.  The 
cupric  oxide  and  asbestos  must  be  dried  by  heating  in  the 
porcelain  crucible  before  use.  Put  about  0.2  g.  of  pure  dry 
sugar-charcoal  [Instructor]  in  a  porcelain  boat,  weigh  the 
boat  with  contents,  and  set  it  in  the  tube  close  behind  the  cupric 
oxide.  Make  a  few  c.c.  of  a  strong  (approximately  30  per 
cent)  solution  of  potassium  hydroxide,  fill  the  bend  of  the 
U-tube  with  it,  and  charge  the  small  tube  beyond  with  frag- 
ments of  solid  caustic  potash.  Test  the  apparatus  with  the 
greatest  care  to  see  that  it  is  absolutely  air-tight  [Instructions]. 
Finally,  immediately  before  starting  the  combustion,  weigh  the 
connected  potash  tubes,  replace  them  in  position,  and  test 
once  more  for  air-tightness. 

Slip  a  cylinder,  made  by  rolling  a  piece  of  wire  gauze,  over 
the  hard  glass  tube,  connect  the  latter  with  the  oxygen  cylin- 
der (or  other  source  of  oxygen),  and  heat  the  part  containing 

33 


34  EQUIVALENT   WEIGHTS  [§35 

the  boat  and  cupric  oxide  with  two  burners  (extra  Bunsen 
burner  from  storeroom).  Turn  on  the  oxygen  with  care  and 
regulate  the  stream  so  that  the  carbon  may  burn  slowly  and 
not  more  than  15-20  bubbles  of  unused  oxygen  escape  per 
minute.  A  more  rapid  stream  will  involve  the  loss  of  carbon 
dioxide.  Heat  the  front  of  the  boat  first  and  let  the  glow, 
caused  by  the  combustion,  travel  along.  The  burning  will  take 
30-45  minutes.  Continue  the  stream  of  oxygen  for  4-5  minutes 
after  the  carbon  is  completely  burned  (why?),  then  disconnect 
the  potash  apparatus  and  weigh  it.  A  more  accurate  result  is 
obtained  by  finally  displacing  the  oxygen  by  air  (why?).  After 
the  tube  has  cooled,  weigh  the  boat  with  any  ash  it  may  con- 
tain. Return  the  cupric  oxide  to  the  bottle. 

The  loss  in  weight  of  the  boat  gives  the  amount  of  car- 
bon; the  gain  in  weight  of  the  potash  apparatus,  the  amount 
of  the  carbon  dioxide.  The  difference  of  these  two  gives  the 
oxygen. 

Calculate  from  your  data  the  weight  of  carbon  combining 
with  8  parts  of  oxygen. 

Wt.  of  ox.  found  :  Wt.  of  carbon  found  :  :  8  :  x. 

This  gives  x,  the  combining  weight  [R  46]  of  carbon.  This 
weight  of  carbon  is  equivalent  [R  49]  to  those  amounts  of  other 
elements  which  likewise  unite  with  8  parts  of  oxygen. 

Assuming  the  atomic  weights  of  carbon  and  oxygen  to  be 
12  and  16  respectively,  calculate  from  your  data  the  formula  of 
carbon  dioxide  [R  57]. 

Make  the  equation  representing  the  action. 

36.  Composition  of  an  Oxide  of  a  Metal  [Quant.  Note  22, 
p.  7].  On  account  of  the  difficulties  attending  the  making, 
the  collecting,  or  the  weighing  of  most  oxides  formed  by  direct 
union,  the  following  indirect  method  is  suggested.  It  consists 
in  converting  a  known  weight  of  a  metal  into  the  nitrate  of  the 
metal  by  the  action  of  nitric  acid,  and  obtaining  the  oxide  by 
decomposition  of  this  salt.  Attempt  no  equations  for  these 
actions. 

a.  Composition  of  an  oxide  of  iron.  Weigh  an  evaporating- 
dish  of  medium  size,  place  in  it  about  1  g.  (12  inches)  of  pure 
iron  wire,  and  weigh  again.  Cover  the  dish  with  a  watch-glass, 
convex  side  downward,  and  add  10  c.c.  of  pure  dilute  nitric 
acid.  Set  the  dish,  covered,  on  the  water  bath  until  the  iron 
has  dissolved,  adding  a  few  drops  of  concentrated  nitric  acid 
if  any  of  the  wire  remains  unattacked  [Instructions].  Then 
rinse  the  cover-glass  carefully  into  the  dish  and  remove  it,  and 
evaporate  the  solution  to  dryness  on  the  water  bath  or  on  a 


§36]  EQUIVALENT  WEIGHTS  35 

beaker  of  boiling  water  [Hood].  When  the  residue  (what  is 
it?)  is  dry,  place  the  dish  on  a  clay  triangle  supported  on  the 
ring-stand  and  heat  carefully  with  a  burner  held  in  the  hand  as 
long  as  any  red  fumes  are  given  off.  During  this  process,  and 
especially  at  first,  great  care  and  patience  must  be  exercised, 
as  too  rapid  heating  may  cause  solid  particles  of  the  product  to 
be  thrown  from  the  vessel.  If  any  crackling  noise  is  observed, 
remove  the  burner  at  once.  When,  after  final  strong  heating 
of  every  part  of  the  material,  red  fumes  or  other  evidence  of 
continued  change  can  no  longer  be  perceived,  allow  the  dish 
and  contents  (?J  to  cool  and  weigh  them.  To  make  sure  that 
the  decomposition  was  complete,  heat  once  more,  cool,  and 
weigh  again.  This  precaution  is  always  necessary  in  experi- 
ments of  this  nature. 

The  difference  of  the  weights  of  the  metal  and  of  the  oxide 
gives  the  weight  of  oxygen  combined  with  the  known  weight 
of  iron. 

Calculate  from  your  data  the  weight  of  iron  (x)  combining 
with  8  parts  of  oxygen. 

Wt.  of  ox.  found  :  Wt.  of  iron  :  :  8  :  x. 

This  is  the  combining  weight  [R  46]  of  iron  in  this  oxide. 
This  weight  of  iron  is  equivalent  [R  49]  to  those  amounts  of 
other  elements  which  likewise  unite  with  8  parts  of  oxygen. 

Assuming  the  atomic  weights  of  iron  and  of  oxygen  to  be  55.9 
and  16,  respectively,  calculate  from  your  data  the  formula  of 
the  oxide  of  iron  [R  57].  What  is  the  name  of  this  oxide?  What 
other  oxides  of  iron  are  known  [R]  ? 

b.  Pure  zinc  (about  1  g.)  may  be  used  instead  of  iron.    The 
manipulation  is  the  same  as  in  35  a.     The  residue  from  evapo- 
ration is  a  syrup-like  body,  however,  which  cannot  be  dried. 
Extra  caution  must,  therefore,  be  used  in  heating  this  to  avoid 
loss  by  spirting. 

Calculate  the  combining  (equivalent)  weight  of  zinc  and  the 
formula  of  the  oxide  as  in  35  a. 

c.  Magnesium  wire  (about  1  g.)  may  be  used  instead  of  zine 
(35  6).     Equal  care  is  required  during  the  evaporation  and 
heating.     Tin  (about  1  g.)  may  also  be  used. 

36.  Equivalent  Weight  of  a  Metal  by  Displacing  Hydrogen 
[Quant.]. 

a.  First  fill  the  pneumatic  trough  and  1-liter  bottle  with 
water  so  that  the  liquid  may  acquire  the  temperature  of  the 
room.  Fit  a  100  c.c.  flask  somewhat  as  in  Fig.  8,  using  in  place 
of  the  thistle-tube  a  dropping-funnel  (see  36  6).  To  carry  a 
doubly-bored  cork  the  mouth  of  the  flask  must  be  rather  wide. 


36  EQUIVALENT   WEIGHTS  [§36 

A  larger  flask  than  100  c.c.  must  not  be  employed  on  account 
of  the  waste  of  acid  its  use  would  entail.  The  stem  of  the 
dropping-funnel  must  reach  to  the  bottom  of  the  flask,  and  the 
inner  end  of  the  L-tube  must  not  project  below  the  bottom  of 
the  cork.  Attach  a  rubber  or  glass  delivery  tube  and  see  that 
the  apparatus  is  air-tight.  Weigh  a  piece  of  chemically  pure 
zinc,  -taking  about  2  g.  Without  detaching  your  platinum  wire 
from  the  glass  rod,  wrap  it  tightly  round  the  zinc  (why)?  and 
allow  the  whole  to  slide  gently  into  the  flask.  Fill  the  appara- 
tus completely,  from  the  top  of  the  stem  of  the  funnel  to  the 
tip  of  the  delivery  tube,  with  water.  Close  the  stopcock  when 
the  bulb  has  almost  emptied  itself.  Invert  the  1-liter  bottle, 
filled  with  water,  on  the  shelf  of  the  pneumatic  trough,  and  put 
the  delivery  tube  in  position. 

Fill  the  globe  of  the  funnel  with  pure  concentrated  hydro- 
chloric acid  [Side-shelf]  and  admit  this  to  the  flask,  a  little  at 
a  time,  in  such  a  way  that  a  steady,  but  not  too  violent,  action 
takes  place.  A  good  deal  will  be  needed  at  first  before  suffi- 
ciently rapid  action  begins  (why?).  When  the  metal  is  entirely 
dissolved,  drive  all  the  gas  over  into  the  bottle  by  pouring  water 
once  more  through  the  funnel  (be  careful  that  no  air  is  carried 
over  with  the  water). 

The  weight  of  the  hydrogen  which  has  been  displaced  by  the 
weighed  quantity  of  zinc  is  to  be  ascertained  in  this  experiment, 
not  by  direct  weighing,  but,  as  follows,  by  measuring  the  volume 
of  the  gas  and  calculating  its  weight  from  this  and  the  density 
of  hydrogen : 

When  the  gas  has  acquired  the  temperature  of  the  water  and 
room,  lower  the  bottle  until  the  level  of  the  water  outside  and 
inside  is  the  same.  If  there  is  still  a  good  deal  of  water  in  the 
bottle,  the  latter  may  have  to  be  inclined  to  accomplish  this 
and  the  following  operation.  Close  the  bottle  with  a  cork  while 
it  is  in  this  position  and  remove  it  from  the  trough.  To  find 
the  volume  of  the  gas,  weigh  (to  the  nearest  gram)  the  bottle 
as  it  stands  on  the  laboratory  scales,  and  also  completely  filled 
with  water,  and  subtract.  Since  1  c.c.  of  water  weighs  approx- 
imately 1  g.  the  number  of  grams  in  this  difference  gives  at  once 
the  number  of  c.c.  of  hydrogen.  Why  is  this  method  of  meas- 
uring the  volume  of  the  water  more  accurate  than  using  the 
graduated  cylinder?  Record  the  temperature  of  the  hydrogen 
by  reading  a  thermometer  hung  in  the  laboratory  close  to  the 
apparatus.  Read  the  barometer,  and  record  the  corrected 
reading  [Note  31,  p.  18].  Since  the  hydrogen  is  mixed  with 
water  vapor,  correct  for  the  latter  by  subtracting  the  aqueous 
tension  (Appendix  II)  at  the  observed  laboratory  temperature 


§38]  EQUIVALENT  WEIGHTS  37 

from  the  corrected  barometric  reading.    This  gives  the  true 
partial  pressure  of  the  hydrogen. 

Reduce  the  volume  of  the  hydrogen,  by  rule,  from  the  ob- 
served temperature  and  partial  pressure  to  0°  and  760  mm. 
Find  by  calculation  (1  liter  weighs  0.09  gr.  at  0°  and  760  mm.) 
the  weight  of  the  hydrogen  obtained.  Calculate  the  equi- 
valent weight  of  zinc,  i.e.,  the  weight  of  the  metal  (x)  which 
displaces  1.008  g.  of  hydrogen: 

Wt.  of  hyd.  :  Wt.  of  zinc  :  :  1.008  :  x. 

Calculate  from  the  result  how  many  equivalent  weights  of 
hydrogen  would  be  displaced  by  65.4  g.;  the  gram-atomic 
weight,  of  zinc.  What  is  the  valence  of  zinc?  How  many  for- 
mula-weights of  hydrogen  chloride  are  required  to  furnish  the 
hydrogen  displaceable  by  one  atomic  weight  of  zinc?  Write 
the  left-hand  side  of  the  equation  in  accordance  with  this 
result. 

Wash  the  trough  carefully  until  it  is  absolutely  free  from 
acid,  and  put  it  away  in  an  inverted  position  to  avoid  rusting. 

b.  The  above  experiment  may  be  performed  with  magne- 
sium (about  0.9  g.),  iron  (about  1.  8g.)y  or  aluminium  (about  0.8 
g.)  in  place  of  zinc. 

In  the  absence  of  a  dropping-funnel,  a  substitute  may  be 
made  by  connecting  a  funnel  with  a  straight  tube  by  means  of 
a  rubber  joint  closed  with  a  pinch  clamp.  Or,  the  aspirator 
(Fig.  7)  may  be  used  here,  the  metal  (half  the  above  quantities), 
water,  and  a  smaller  tube  containing  the  acid  being  placed  in 
the  test-tube,  and  the  mixing  being  effected  by  inclining  the 
bottle  after  the  apparatus  is  connected. 

37,  Inter  -Equivalence  of  Equivalent  Weights  (Law  of  Recip- 
rocal Proportions) .      If  35  b  was  performed,  compare  the  quan- 
tity of  zinc  which  combined  with  8  g.  of  oxygen  with  that  which 
in  36  a  was  found  to  displace  1.008  g.  of  hydrogen.    If  they  are 
identical,   these  two  quantities  of  oxygen  and  hydrogen  are 
chemically  equivalent   and   may   combine   with  one  another. 
What  substance  has  precisely  this  composition? 

If  magnesium  was  used,  in  36  b,  compare  the  quantity  with 
that  combining,  in  35  c,  with  8  g.  of  oxygen  and  answer  the 
same  question. 

38,  Combining    Weights    of    Zinc    and    Chlorine    [Quant.]. 
(From  Torrey's  Elementary  Studies.)     Weigh  an   evaporating- 
dish  of  medium  size  and  place  in  it  about  2  g.  of  pure  zinc.     Add 
a  little  diluted  (1  Aq. :  2  acid),  pure,  concentrated  hydrochloric 
acid  [Side-shelf]  and   cover  with  a  watch-glass,   convex  side 
downward.    If  the  action  is  very  slow,  the  tip  of  a  platinum 


38  EQUIVALENT   WEIGHTS  [§  39 

wire  may  be  placed  in  contact  with  the  zinc.  Maintain  a  brisk 
action  by  further  additions  of  concentrated  hydrochloric  acid 
in  very  small  amounts  at  a  time.  Final  excess  of  the  acid  should 
be  avoided,  as  time  will  be  lost  in  the  subsequent  evaporation. 
When  the  metal  is  completely  dissolved,  rinse  the  cover-glass 
and  platinum  wire  carefully  into  the  porcelain  dish  and  remove 
them.  Allow  the  solution  to  evaporate  as  far  as  possible  on 
the  water  bath  or  on  a  beaker  of  boiling  water  [Hood].  Now 
place  the  dish  on  the  ring-stand,  and,  using  a  small  Bunsen 
flame,  allow  the  syrup-like  solution  to  evaporate  slowly  to 
dryness.  Then  heat  the  white  mass  to  the  point  at  which 
it  has  completely  melted  and  no  further.  The  best  way  to 
achieve  this  with  the  minimum  rise  in  temperature  is  to  let  the 
Bunsen  flame  play  on  the  surface  from  above.  Overheating 
must  be  avoided,  because  the  product  is  volatile  at  high  tem- 
peratures. The  moment  the  dish  has  so  far  cooled  that  the 
hand  can  be  borne  upon  the  bottom,  wipe  the  dish  carefully 
and  weigh  it.  The  substance  absorbs  moisture  greedily  from 
the  atmosphere,  hence  expedition  is  required  in  cooling  and 
weighing  if  accurate  results  are  to  be  obtained.  To  insure 
accuracy,  the  melting,  cooling,  and  weighing  should  be  repeated, 
and  the  lower  result  taken  as  correct. 

Calculate,  from  the  data  obtained  in  this  experiment,  how 
much  chlorine  combines  with  the  equivalent  weight  of  zinc 
found  in  36  a.  This  amount  is  the  equivalent  weight  of 
chlorine  (x) : 

Wt.  of  zinc :  Wt.  of  chlor.  :  :  Equiv.  of  zinc  :  x. 

Assuming  the  atomic  weights  of  zinc  and  chlorine  to  be  65.4 
and  35.45  respectively,  determine  the  formula  of  zinc  chloride. 

Express  the  whole  action  of  hydrochloric  acid  on  zinc  in 
symbols  by  making  the  equation  in  accordance  with  these 
conclusions.  Which  of  the  factors  in  the  equation  have  you 
determined  experimentally,  and  which  not?  What  law  do  we 
use  in  assuming  that  the  undetermined  factors  are  correct? 

39.  Combining   Weights    of   Lead   or   Silver   and   Chlorine. 
From  the  weights  of  lead   (9  a)   or  silver   (96)   and    chlorine 
found  to  combine,   calculate  the  formula  of  lead   (or  silver) 
chloride. 

40,  Multiple  Proportions  [Quant.]. 

a.  [Two  students  working  together].  Fit  a  hard  glass  tube 
with  corks  through  which  pass  short  pieces  of  narrow  glass 
tubing  (Fig.  9).  Fix  the  tube  in  a  clamp  upon  the  ring-stand, 
attaching  the  clamp  close  to  one  end  so  that  the  rubber  cover- 
ing of  the  clamp  may  be  away  from  the  central  part  which  is  to 


§40]  EQUIVALENT   WEIGHTS  39 

be  heated.  Make  sure  that  the  apparatus  is  air-tight.  Dry 
some  pulverized  cupric  oxide  by  heating  it  in  a  hard  glass  test- 
tube.  Weigh  two  clean,  dry,  porcelain  boats,  and  place  in  one 
about  1.5  g.  of  the  cupric  oxide  and  in  the  other  2.5  g.  or  more 
of  cuprous  oxide  *  [From  Instructor]  and  weigh  each  again.  In 
recording  the  weights  and  in  handling  the  boats  be  careful  to 
distinguish  the  one  from  the  other.  Place  the  boats  in  the 
hard  glass  tube,  so  that  the  points  of  the  boats  touch  in  the 
center  of  the  tube.  Connect  the  end  nearest  to  the  cuprous 
oxide  with  a  source  of  dry  hydrogen  (Kipp's  apparatus  and 
drying-bottle,  or  laboratory  supply). 

Pass  a  gentle  stream  of  hydrogen  through  the  apparatus 
until  a  test  (?)  shows  that  the  air  has  all  been  displaced.  Re- 
duce (why?)  the  speed  of  the  gas  until  the  bubbles  in  the  wash- 
ing-bottle can  easily  be  counted.  Now  heat  the  boats  moder- 
ately, beginning  with  that  containing  the  cuprous  oxide.  What 
collects  in  the  cooler  end  of  the  tube?  Where  does  it  come 
from?  When  the  action,  which  requires  10-15  minutes,  is 
finished,  allow  the  boats  to  cool  in  a  stream  of  hydrogen.  Weigh 
the  boats  and  contents  (?),  taking  care  not  to  interchange 
them.  To  ascertain  whether  the  action  is  complete,  heat  the 
boats  once  more  in  hydrogen,  cool,  and  weigh  again. 

Determine  by  difference  the  weights  of  oxygen  and  copper  in 
each  case,  and  calculate  from  the  data  how  much  copper  is* 
combined  with  8  parts  of  oxygen  in  each  of  the  two  oxides. 
What  is  the  ratio  of  the  two  values  of  copper?  Show  that  the 
result  illustrates  the  law  of  multiple  proportions. 

Assuming  16  and  63.6  to  be  the  atomic  weights  of  oxygen 
and  of  copper,  respectively,  calculate  from  the  data  the  formula 
of  each  oxide.  Construct  the  equations  representing  the 
action  of  hydrogen  upon  each  oxide. 

6.  Pure  lead  dioxide  and  pure  lead  monoxide  may  be  used 
as  in  a,  if  available.  The  monoxide,  however,  absorbs  carbon 
dioxide  readily  from  the  air,  and  therefore  does  not  keep  well. 
The  experiment  must,  therefore,  be  tried  by  the  instructor 
before  the  material  on  hand  is  given  to  the  class.  Lead  mon- 
oxide is  more  difficult  to  reduce  than  the  dioxide.  The  heat- 
ing in  a  stream  of  hydrogen  must  be  repeated  to  constant 
weight. 

c.  If  the  quantitative  decomposition  of  potassium  chlorate 
(15  6)  was  carried  out,  dried  potassium  perchlorate  may  be 
decomposed  in  the  same  way  and  the  results  compared.  Weigh 
an  open,  long,  hard  glass  test-tube.  Place  in  it  about  1  g.  of 

*  Pure  cuprous  oxide  (Kahlbaum's)  can  be  kept  successfully  if  sealed 
up  in  small  bottles  which  are  not  opened  until  needed. 


40  EQUIVALENT  WEIGHTS  [§  41 

potassium  perchlorate  and  weigh  again.  Then  heat  the  tube 
and  drive  off  the  oxygen  slowly,  and  weigh  again.  Heat 
strongly  once  more,  to  constant  weight.  Ascertain  by  differ- 
ence the  weights  of  potassium  chloride  (residue)  and  of  oxygen. 

The  formula  of  the  perchlorate  is  KC10X/.  Calculate  from 
your  data  how  much  oxygen  ((V)  is  combined  with  74.6  g.,  the 
formula-weight,  of  potassium  chloride  (KC1).  This  result,  the 
formula-weight  of  the  oxygen,  will  be  a  multiple  of  16.  Com- 
pare this  formula-weight  of  oxygen  with  that  found  in  the 
experiment  with  potassium  chlorate,  and  show  how  the  results 
illustrate  the  law  of  multiple  proportions.  Find  the  formula 
of  potassium  perchlorate  and  write  the  equation  for  the  decom- 
position of  the  compound. 

41.  Dulong  and  Petit's  Law.  According  to  Dulong  and 
Petit  [R  211],  if  the  correct  atomic  weight,  when  it  has  been 
found,  is  multiplied  by  the  specific  heat  of  the  element  in  the 
solid  form,  the  product  is  a  number  which  in  most  cases  lies 
between  6  and  6.8. 

Take  the  values  of  such  combining  weights  or  equivalents 
as  you  have  found  experimentally,  viz.,  iron  (36  a,  36  6),  zinc 
(35  6,  36  a);  magnesium  (35  c,  36  6),  aluminium  (36  6),  silver 
(39),  copper  (40  a,  two  values),  or  lead  (39,  one  value,  and  40  b, 
two  values),  and  multiply  each  by  the  corresponding  specific 
"heat  (Appendix  III).  If  the  result  is  about  6.4,  the  atomic 
weight  is  the  same  as  the  equivalent  weight.  If  not,  multiply 
the  equivalent  weight  by  the  smallest  integer  which  will  bring 
the  final  product  within  the  limits  6  to  6.8.  The  integer  used 
is  the  valence  of  the  element,  and  the  product  of  the  equivalent 
weight  and  the  valence  is  the  atomic  weight.  Show  the  working 
hi  your  notes  and  give  a  list  of  the  atomic  weights  and  valences 
found.  In  the  case  of  copper  or  lead,  distinguish  the  valences 
in  the  two  compounds. 


CHAPTER  VIII. 

BROMINE,   IODINE,   FLUORINE,    AND   THEIR   COMPOUNDS 
WITH    HYDROGEN. 

CHLORINE  (Chap.  VI)  and  the  elements  to  be  studied  in  this 
chapter  form  a  group  having  very  similar  properties,  and  are 
called  the  halogens.  Recall  the  facts  about  chlorine  and 
hydrogen  chloride,  and  use  them  as  a  guide  in  trying  to  under- 
stand the  chemistry  of  the  rest  of  the  group.  Remember 
particularly  that  chlorine  is  colored,  has  a  powerful  odor,  and 
does  not  cause  fumes  in  moist  air;  and  that  hydrogen  chloride 
is  colorless,  and  causes  dense  fumes  in  moist  air.  The  corre- 
sponding substances  throughout  the  group  may  be  expected  to 
present  properties  like  these.  Thus,  the  elements  are  all  colored 
substances,  the  hydrogen  compounds  are  all  colorless  and  fume 
in  moist  air.  The  hydrogen  compounds,  hydrogen  chloride, 
hydrogen  bromide,  etc.,  are  known  as  the  hydrogen  halides. 

42.  Preparation  of  Bromine  [Hood],     Powder  about  1  g.  of 
potassium  bromide,  mix  it  in  the  mortar  intimately  with  about 
2  g.  of  pulverized  manganese  dioxide,  and  place  the  mixture  in 
a  test-tube.     In  a  second  test-tube  dilute  2-3  c.c.  of  concen- 
trated sulphuric  acid  [Desk]  with  half  its  volume  of  water  (add  the 
acid,  cautiously,  to  the  water),  and  mix  with  the  contents  of  the 
first  test-tube  enough  of  this  solution  to  moisten  the  materials 
thoroughly,  and  no  more.     After  allowing  the  mass  to  stand 
for  a  few  minutes,  apply  a  gentle  heat  to  the  tube,  and  note 
the  color  and  behavior  of  the  vapors  evolved  (?).     Apply  a 
strip  of  filter  paper  moistened  with  a  starch-potassium  iodide 
emulsion  (29  a)  to  the  mouth  of  the  tube  (?). 

What  other  materials  might  be  substituted  for  the  potassium 
bromide  in  the  above  experiment? 

43.  Properties  of  Bromine. 

Shake  up  one  drop  of  bromine  [CARE.  Do  not  spill  upon  the 
hands]  with  10  to  15  c.c.  of  water  in  a  test-tube,  and  divide  the 
solution  ("bromine-water")  between  four  test-tubes. 

a.  To  one  of  these  add  1-2  c.c.  of  ether,  and  shake  (?).  Note 
the  relative  solubility  of  bromine  in  ether  and  in  water  as  dis- 
played by  the  depth  of  color  in  each  layer  (26  g}.  To  the 
second  add  carbon  disulphide  (?),  and  to  the  third  chloro- 
form (?),  observing  as  before.  To  about  10  c.c.  of  starch 

41 


42  BROMINE,  IODINE,  FLUORINE  [§  44 

emulsion  add  a  few  drops  from  the  fourth  test-tube  (?)  [R  230 
and  see  result  of  47  b,  below], 

b.  Fit  up  an  apparatus  to  generate  a  small  amount  of  chlorine 
[Hood],  using  a  side-neck  test-tube  instead  of  the  flask  in  Fig. 
11  (p.  29).  If  chlorine-water  is  available,  it  may  be  used 
instead  of  the  gas. 

Dissolve  a  single,  very  small  crystal  of  potassium  bromide  in 
a  few  c.c.  of  water  in  a  test-tube.  Add  several  drops  of  carbon 
disulphide,  and  then  pass  a  few  bubbles  of  chlorine  through  the 
solution,  or  add  a  few  c.c.  of  chlorine-water  (?).  Shake,  and 
notice  the  appearance  of  color  in  the  carbon  disulphide  (?). 
Infer  from  this  result  'the  relative  activities  of  chlorine  and 
bromine  (?).  The  result  measures  the  relative  affinity  of 
chlorine  and  bromine  for  what  elements? 

The  chlorine  generator,  if  used,  is  required  again  in  47  c, 
which  may  be  performed  at  once,  before  the  apparatus  is  taken 
apart  and  cleaned.  Prepare  also  5  c.c.  of  saturated  chlorine- 
water,  if  not  furnished  on  the  side-shelf,  cork  it  up  in  a  test- 
tube,  and  set  it  aside  in  a  dark  place  for  use  in  46  g  and  50  a. 
44.  Preparation  of  Hydrogen  Bromide. 

o.  Pulverize  about  1  g.  of  potassium  bromide,  place  it  in  a 
test-tube,  and  cover  with  concentrated  phosphoric  acid  solu- 
tion. Notice  the  apparent  slowness  of  the  action  on  account 
of  the  insolubility  (physical)  of  the  compound  in  the  liquid 
(sodium  bromide  is  much  more  soluble,  and  should  be  used,  if 
available).  Warm,  if  necessary.  Observe  the  odor  (?),  and 

insert  a  rod  dipped  in  ammonium 

hydroxide  solution  (?)  [Note  33, 

p.  31]. 

For   the    action    of    sulphuric 

acid  with  a  bromide,  see  62  b. 
b.   Fit  up  a  250  c.c.  flask  with 

a  dropping-funnel  and  exit  tube, 

and  connect  with  a  U-tube  (Fig. 

13).      Render  the  apparatus  air- 
Fig.  13  tight.      Fill    the     U-tube    with 

dry,  broken  glass  or  porcelain, 
mixed  with  a  little  red  phosphorus  (why?).  Connect  the 
other  limb  of  the  U-tube  with  a  second,  larger  U-tube  [Store- 
room] containing  about  10  c.c.  of  water.  Place  about  5  g. 
of  red  phosphorus  mixed  with  twice  its  weight  of  sand  in 
the  flask,  add  5  c.c.  of  water,  and  mix  by  shaking.  Pour 
into  the  globe  of  the  funnel  about  8  c.c.  of  bromine  [EXTREME 
CARE.  Do  not  spill  upon  the  hands  (Note  16,  p.  2)].  Allow 
the  bromine  to  flow  drop  by  drop  on  to  the  phosphorus,  and 


§  47]  BROMINE,  IODINE,  FLUORINE  43 

let  the  gas  dissolve  in  the  water  in  the  second  U-tube.  A 
large  volume  of  air  is  expelled  before  the  hydrogen  bromide 
reaches  the  second  U-tube.  Disconnect  the  second  U-tube 
and  reserve  the  solution  for  use  in  46. 

Try  the  effect  of  moist  air  upon  the  gas  issuing  from  the 
main  apparatus  (?).  Hold  in  the  gas  a  rod  dipped  in  ammo- 
nium hydroxide  (?). 

45.  Properties  of  Aqueous  Hydrobromic  Acid.     Divide  the 
solution  into  seven  portions  and  examine  its  behavior  toward 
(a)   litmus  (?),  (6)  zinc  in  contact  with  a  platinum  wire  (?), 
(c)  silver    nitrate    solution    (?),    (d)  mercurous    nitrate    solu- 
tion (?),  (e)  lead  nitrate  solution  (?),  (/)  powdered  manganese 
dioxide  (warm)   (?).     Boil  c,  d,  and  e,  after  pouring  away  the 
supernatant  liquid  and  adding  more  water  to  each  (?).     Com- 
pare these  results  with  those  found  in  the  case  of  hydrochloric 
acid  (32). 

g.  To  the  seventh  portion  add  a  few  drops  of  chlorine-water 
(43  6),  a  few  drops  of  carbon  disulphide,  and  shake  (?).  This 
result  indicates  the  relative  affinities  of  chlorine  and  bromine 
for  what  elements,  and  how? 

46.  Preparation  of  Iodine.     Prepare  a  mixture  of  potassium 
iodide  (1  g.)  and  manganese  dioxide  (2  g.)  exactly  as  in  42, 
place  it  in  an  evaporating-dish,  and  moisten  (2-3  drops)  with 
sulphuric  acid  diluted  with  water  (1  Aq.:  2  acid).     Cover  the 
dish  with  a  watch-glass  (partially  filled  with  cold  water  to  cool 
the  surface  presented  to  the  vapors)  and  warm  very  gently. 
After  a  time  examine  the  sublimate  [Note  34,  below].     Expose 
a  strip  of  filter  paper,  moistened  with  starch  emulsion  alone, 
to  the  vapors   (?).     Recall  the  interaction  of  chlorides  with 
manganese  dioxide  and  sulphuric  acid  [R  172]. 

What  other  materials  might  be  substituted  for  potassium 
iodide  in  preparing  iodine? 

Note  34.  —  Stains  upon  the  fingers  caused  by  iodine  may  be 
removed  by  rubbing  with  sodium  thiosulphate  solution  ("hypo"). 

47.  Properties  of  Iodine.     Shake  a  few  crystals  of  iodine 
vigorously  [Note  34]  with  about  10  c.c.  of  water  in  a  test-tube. 
Pour   the   clear  liquid   off,   dividing  it  equally  between  four 
test-tubes. 

a.  Add  to  one  portion  a  few  drops  of  chloroform,  to  another 
ether,  and  to  a  third  carbon  disulphide.  Shake  each  vigor- 
ously and  note  the  relative  solubility  (estimated  by  depth  of 
color)  of  iodine  in  water  as  compared  with  that  in  each  of  the 
other  solvents  (?). 


44  BROMINE,  IODINE,  FLUORINE  [§  48 

b.  Take  15  c.c.  of  starch  emulsion  and  add  the  fourth  portion 
to  it  (?).     Pour  the  mixture  info  the  graduated  cylinder  and 
add  water  so  long  as  a  sample  poured  out  into  a  test-tube 
continues  to  show  an  easily  perceptible  color.     Why  is  the  use 
of  starch  considered  to  be  a  delicate  test  for  iodine?    Does  it 
show  the  presence  of  iodine  in  combination  (48  6)  ? 

c.  Repeat  43   b,  using  a  very  small  crystal  of  potassium 
iodide  (?).     Infer  the  relative  activities  of  chlorine  and  iodine. 
The  result  measures  the  relative  affinities  of  these  two  halogens 
for  what  elements? 

d.  Repeat  c,  using  potassium  iodide,  but  substituting  bro- 
mine-water for  chlorine.     In  what  order  do  the  halogens  stand, 
in  respect  to  activity,  and  why  do  you  place  them  in  that 
order? 

48.  Preparation  of  Hydrogen  Iodide  [Hood]. 

a.  Repeat  44  a  with  potassium  iodide  or  sodium  iodide  (?). 

b.  Use  the  apparatus  in  Fig.  13.     Place  in  the  flask  a  mix- 
ture of  finely   powdered   iodine   (20  g.)   and   red   phosphorus 
(3  g.)  intimately  mixed  in  the  mortar.     Charge  the  U-tubes  as 
in  44  6.     Place  a  little  water  in  the  dropping-funnel  (or  sub- 
stitute, 36  6),  warm  the  materials  in  the  flask  very  slightly 
(EXTREME  CAUTION!]  by  waving  the  Bunsen  flame  once  or 
twice  under  the  vessel,  and  allow  the  water  to  drop  very  slowly 
upon  them  (?).     After  the  air  has  all  been  expelled,  and  the 
solution  in  the  second  U-tube  has  become  sufficiently  concen- 
trated, remove  the  second  U-tube.     Test  the  issuing  gas  with 
moist  air  (?)  and  with  ammonia  (?)  as  in  44  b.     Hold  in  the 
gas  a  piece  of  filter  paper  dipped  in  starch  emulsion  alone  (?). 
Explain.     Reserve  the  contents  of  the  second  U-tube  for  use  in 
60  a. 

49.  Preparation  of  Hydriodic  Acid  [Hood].     Place  5  g.  of 
powdered  iodine  with  50  c.c.  of  water  in  a  small  flask  provided 
with  a  cork  and  an  L-tube  extending  to  the  bottom.     Pass 
hydrogen  sulphide  from  a  Kipp's  generator,  or  from  the  labora- 
tory supply,  through  the  mixture,  loosening  the  cork  once  or 
twice  at  first  to  permit  the  air  to  be  displaced  by  the  gas,  until 
the  iodine  is  all  gone  and  the  solution  no  longer  becomes  brown 
on  being  shaken.     Agitate  constantly  to  hasten  the  process. 
Describe  what  happens.     Warm  and  filter  the  solution. 

Obtain  a  distilling-flask  and  condenser  [Storeroom]  and  distil 
the  filtvate  fractionally  (Fig.  14),  collecting  first  the  part  that 
comes  over  at  100°,  then  the  parts  boiling  between  100-103°, 
103-106°,  and  so  forth.  Use  a  very  small  flame,  and  be  careful 
not  to  allow  it  to  reach  the  walls  of  the  flask  above  the  liquid, 
or  breakage  will  take  place.  A  large  flame  may  not  only  crack 


50] 


BROMINE,  IODINE,  FLUORINE 


45 


the  flask,  but  may  also  cause  the  thermometer  to  show  a  higher 
temperature  than  it  could  acquire  from  the  vapor  alone.  Stop 
when  the  liquid  is  nearly  all  distilled  off.  Note  the  highest 


Fig.  I4 

temperature  reached.  Pour  the  residue  into  a  test-tube  and 
keep  the  series  for  use  in  50  b. 

What  substance  causes  the  color  of  the  higher  fractions  and 
of  the  residue?  Confirm  your  conclusion  by  a  suitable  test 
(47).  How  is  this  colored  substance  formed? 

50.   Properties  of  Hydriodic  Acid. 

a.  If  48  b  was  done,  carry  out  the  same  experiments  with 
the  solution  as  were  made  with  the  solution  of  hydrobromic 
acid  in  45  (?).     Compare  the  results  with  those  of  45  (?). 

b.  If  49  was  done,  add  silver  nitrate  solution  to  each  of  the 
fractions  above  100°  obtained  in  49,  using  only  a  part  of  the 
liquid  in  the  case  of  the  two  with  the  highest  boiling-points. 
At  what  temperature  did  the  most  concentrated  solution  of 
hydrogen   iodide    come    over?    What   peculiarity   of   aqueous 
hydriodic  acid  does  the  result  indicate?    What  other  solutions 
show  the  same  peculiarity  [R  182,  232,  239,  241,  387,  440]? 

Place  a  piece  of  zinc,  in  contact  with  a  platinum  wire,  in  the 
remainder  of  one  of  the  higher  fractions  (?).  Test  the  other 
with  litmus  paper  (?),  and  then  add  pulverized  manganese 
dioxide,  and  warm  (?). 


46  BROMINE,  IODINE,  FLUORINE          [§  51 

61.  Hydrogen  Fluoride.  Cover  a  square  of  glass  with  a 
thin  layer  of  paraffin  by  warming  it  very  cautiously  far  above 
a  Buusen  flame  and  rubbing  it  on  one  side  with  solid  paraffin. 
Moisten  about  3  g.  of  fluorspar  in  a  leaden  dish  [Storeroom] 
with  concentrated  sulphuric  acid  (do  not  cover  with  the  acid). 
With  the  end  of  a  file  draw  some  design  upon  the  paraffin- 
coated  side,  thus  exposing  parts  of  the  glass  to  the  action  of 
the  vapor.  Now  cover  the  leaden  dish  with  the  glass,  paraffin 
side  down,  and  set  it  in  a  moderately  warm  place,  but  not  so 
warm  that  paraffin  may  be  likely  to  melt.  After  half  an  hour 
or  more  remove  the  glass  cover,  warm,  and  wipe  off  the  melted 
paraffin  with  filter  paper  (?).  Write  equations  representing 
the  action,  and  state  what  becomes  of  each  of  the  constituents 
of  the  glass  [R  243,  521].  Try  the  test  of  a  rod  dipped  in  am- 
monium hydroxide  and  held  over  the  contents  of  the  lead 
dish  (?).  Does  the  gas  fume  with  moist  air?  What  sub- 
stances, beside  fluorspar,  would  serve  the  purpose  of  this  ex- 
periment? Why  could  not  hydrochloric  acid  or  nitric  acid  be 
substituted  here  for  sulphuric  acid?  What  acid  that  we  have 
employed  could  be  used  here? 

How  may  fluorine  be  liberated  from  a  fluoride?  Why  can 
it  not  be  isolated  from  fluorides  by  the  action  of  oxidizing 
agents,  as  was  the  case  with  the  other  halogens? 

52.  Reducing  Action  of  Hydrogen  Iodide  and  Hydrogen 
Bromide  [Hood].  In  connection  with  this  experiment,  it  must 
be  kept  in  mind  that  an  odor  similar  to  that  of  rotten  eggs 
shows  the  presence  of  hydrogen  sulphide  (49),  and  an  odor  of 
burning  sulphur  the  presence  of  sulphur  dioxide  (13  a). 

a.  Pulverize  finely  about  1  g.  of  potassium  iodide,  place  it 
in  a  test-tube,  and  moisten  with  one  or  two  drops  of  concen- 
trated sulphuric  acid  (?).  If  too  much  acid  has  been  taken, 
start  again.  Warm  gently.  Investigate  the  result,  which 
furnishes  a  mixture  of  gases,  as  follows : 

a.  Breathe  across  the  mouth  of  the  test-tube  to  ascertain 
the  effect  of  the  gas  on  moist  air  (?).  What  gases  previously 
made  showed  the  same  behavior?  What  do  you  infer  in  this 
case?  To  confirm  this  conclusion,  lower  a  glass  rod  dipped  in 
ammonium  hydroxide  into  the  test-tube  (?). 

ft.  Is  any  characteristically  colored  vapor  (?)  mixed  with 
the  gas  recognized  in  a?  Can  you  observe  any  other  property 
which  identifies  the  substance?  By  what  kind  of  chemical 
action  could  this  colored  substance  be  formed  from  the  product 
identified  in  a?  By  what  name  is  such  a  reaction  known? 
Was  there  any  corresponding  product  formed  when  sulphuric 
acid  acted  upon  a  chloride? 


§  53]  BROMINE,  IODINE,  FLUORINE  47 

7.  Can  you  recognize  still  another  (gaseous)  product  by  its 
odor? 

The  work  in  a  and  £  and  7  leads  to  the  recognition  of  three 
gaseous  or  vaporous  products.  Do  not  attempt  to  put  all  of 
these  in  one  equation.  Construct  an  equation  for  the  forma- 
tion from  the  original  materials  of  the  gas  recognized  in  a 
(primary  action),  and  make  a  separate  equation  for  the  forma- 
tion of  the  other  two  products  from  the  interaction  of  sulphuric 
acid  with  the  gas  recognized  in  a  (secondary  action).  What 
two  properties  of  sulphuric  acid  and  what  property  of  hydrogen 
iodide  are  illustrated  by  this  set  of  observations? 

In  case  the  above  directions  are  not  followed  implicitly,  and 
large  pieces  of  potassium  iodide  are  taken,  or  too  much  sul- 
phuric acid  is  used,  still  another  gas  (sulphur  dioxide)  may  be 
formed  along  with  or  instead  of  one  of  the  above,  and,  in  addi- 
tion, a  sublimate  of  free  sulphur  may  be  seen  on  the  tube 
[R  237]. 

b.  Repeat  the  work  in  a,  using  powdered  potassium  bromide 
instead  of  the  iodide,  and  answer  the  same  questions. 

63.  Identification  of  Halogen  Compounds.  Imagine  that 
there  are  given  to  you  four  white  substances,  and  that  you  know 
them  to  be  the  fluoride,  chloride,  bromide,  and  iodide  of  some 
metal.  State  what  experiments  you  would  make,  and  what 
reasoning  you  would  use,  in  order  positively  to  identify  the 
halogen  constituents  of  each.  In  two  of  these  cases,  two  dif- 
ferent actions  have  been  encountered  in  this  chapter  and  might 
be  used,  and  in  the  other  two  cases  only  one.  Still  another  kind 
of  action  might  readily  be  thought  of  [R  63,  311].  Negative 
results,  say  by  showing  that  one  is  not  a  chloride,  bromide,  or 
iodide,  and  is  therefore  a  fluoride,  must  be  confirmed  by  a 
positive  experimental  test. 

If  the  four  hydrogen  halides  were  given  you  in  gaseous  con- 
dition in  four  jars,  how  should  you  proceed  by  chemical  means 
to  identify  each? 


CHAPTER  IX. 

DOUBLE  DECOMPOSITION.   OXYGEN  COMPOUNDS  OF  THE 
HALOGENS.   HYDROGEN  PEROXIDE. 

64.   Radicals  and  Double  Decomposition. 

a.  To  a  few  drops  of  potassium  chloride  solution  add  silver 
nitrate  solution   (?).     What  kind  of  chemical  interaction  do 
salts   usually  show  in  solution  [R  264.     See  Note  4,  p.  1]  ? 
Write  the  equation  for  this  action.     How  can  we  tell  whether 
the  precipitate  is  silver  chloride,  or  potassium  nitrate,  or  both? 
Which  is  it  (Appendix  IV)?     What  was  the  interaction  of 
silver  nitrate  with  hydrochloric  acid  (32  #)?    To  a  few  drops 
each  of  solutions  of  two  other  chlorides,  such  as  ferric  chloride 
and  calcium  chloride,  add  a  little  silver  nitrate  solution  (?). 
To  find  out  whether  all  substances  containing  chlorine  give 
silver  chloride  in  this  way,  try  a  few  drops  of  potassium  chlorate 
solution  with  the  same  silver  compound  (?).     State  now  what 
radical  a  substance  must  contain  in  order  that,  with  silver 
nitrate,  it  may  yield  silver  chloride  (?). 

b.  To  a  few  drops  of  silver  sulphate  solution  add  a  solution 
of  any  chloride  (?).     To  find  out  whether  all  substances  con- 
taining silver  yield  silver  chloride  in  this  way,  take  a  few  drops 
of  silver  nitrate  solution  in  each  of  two  test-tubes.     To  the 
one  portion  add  some  ammonium  hydroxide,  and  so  obtain  a 
solution   of   ammonio-silver  nitrate    (Ag(NH3)2N03).     To   the 
other  add  some  potassium  cyanide  solution  [CAUTION!  POISON!] 
until  the  liquid  is  clear  [Note  35,  below],  and  so  obtain  a  solu- 
tion of  potassium  argenticyanide  (KAg(CN)2).     Now  add  to 
each  of  these  a  solution  of  sodium  chloride  (?) .    Is  the  silver 
radical  present?    Do  all  substances   containing  silver,   when 
mixed  with  a  chloride,  give  silver  chloride?    Which  compounds 
alone  give  silver  chloride  by  double  decomposition? 

c.  Which  substances  alone  will,  by  addition  of  mercurous 
nitrate,   give   mercurous  bromide    (45  d)?    Which   substances 
alone  will,  by  addition  of  silver  nitrate,  give  silver  iodide  (60  a 
and  6)?    Which  substances  alone  will,  by  addition  of  an  acid, 
give  hydrogen  chloride  (31)?     Name  the  classes  of  substances 
which  are  composed  of  radicals,  and  commonly  interact  by 
double  decomposition. 

Note  35.  —  An  insoluble  body  will  not   dissolve  as  such  merely 
because  of  the  addition  of  an  excess  of  the  precipitant,  or  even 

48 


§56]  DOUBLE  DECOMPOSITION  49 

because  of  the  introduction  of  a  different  reagent.  When  an 
insoluble  body  appears  to  go  into  solution,  the  phenomenon  indi- 
cates that  the  substance  added  has  interacted  chemically  with  the 
insoluble  substance  and  has  produced  a  new  substance  which  is 
soluble. 

65.  Chemical  Equilibrium  in  Double  Decomposition. 

a.  When  solutions  of  two  substances,  each  composed  of  two 
radicals,  are  mixed,  and  no  precipitate  is  observed,  interaction 
nevertheless  occurs.  Why  was  no  precipitate  observed  when 
solutions  of  silver  nitrate  and  potassium  chlorate  (64  a)  were 
mixed?  To  answer  this  question,  write  the  equation  for  the 
double  decomposition  which  might  occur,  and  consider  the 
solubilities  of  the  products  (Appendix  IV).  A  similar  case 
where  the  presence  of  the  products  is  easily  shown  may  now 
be  studied  (see  6). 

6.  Place  10  c.c.  of  water  in  each  of  two  test-tubes,  add  to 
one  a  single  drop  of  ammonium  thiocyanate  solution,  and  to 
the  other  a  single  drop  of  ferric  chloride  solution.  Now  mix 
the  solutions  (?).  Write  the  equation  for  the  action  which 
may  be  assumed  to  have  occurred.  Is  there  any  evidence  that 
interaction  has  taken  place?  Which  of  the  four  is  the  colored 
substance?  Use  the  mixture  for  c. 

c.  When  no  precipitate  is  formed,  is  an  action  like  the  above 
(a  or  6)  complete?  To  answer  this  question,  divide  the  mix- 
ture from  6  equally  between  four  test-tubes.  Keep  one  for 
reference.  To  the  second  add  one  drop  of  ferric  chloride  solu- 
tion (?),  and  to  the  third  a  drop  of  ammonium  thiocyanate 
solution  (?).  Interpret  the  result.  Now  add  to  the  fourth 
tube  a  few  drops  of  ammonium  chloride  solution  (?)  and  explain. 

What  other  action  have  we  shown  to  be  reversible  (33)  ?  All 
double  decompositions  of  substances  composed  of  radicals  are 
reversible,  like  these  two.  They  are  also  often  far  from  com- 
plete, when,  as  in  the  present  instance,  precipitation  does  not 
occur.  Why  does  precipitation  tend  to  make  the  action  more 
nearly  complete? 

66.  Hypochlorous  Acid  and  Hypochlorites  [Hood].     Fit  up 
a  chlorine  apparatus  (29  6)  capable  of  delivering  a  large  amount 
of  chlorine  and  make  sure  that  it  is  air-tight.     Use  the  same 
source  of  chlorine  in  56  and  57.     Between  experiments,  immerse 
the  end  of  the  exit  tube  in  sodium  hydroxide  solution,  and 
allow  none  of  the  gas  to  escape  into  the  room. 

a.  Make  an  aqueous  solution  of  chlorine  in  a  ^test-tube. 
Retain  a  few  drops  of  this  for  use  in  6,  and  place  hi  the  re- 
mainder some  litmus  paper,  paper  with  printing  [R  476]  and 
pen  [R  754]  and  pencil  [R  475]  marks  upon  it,  and  a  piece  of 


50  DOUBLE  DECOMPOSITION  [§57 

colored  calico.  Observe  the  effect  on  each.  Explain  [R  176. 
269]. 

6.  To  a  few  drops  of  chlorine-water  add  a  drop  of  indigo 
solution  [R  269]  (?). 

c.  Place  about  5  g.  of  quicklime  in  a  small  beaker,  add  a 
few  c.c.  of  water,  warm  slightly,  and  allow  to  slake  (?).  Now 
add  a  little  more  water  to  make  a  thin  paste,  and  pass  chlorine 
into  the  mixture  for  10-15  minutes  (?),  keeping  the  vessel  cool 
by  surrounding  it  with  cold  water  (why?)  and  stirring  the  con- 
tents during  the  process.  Filter  the  paste,  with  the  addition 
of  some  water  if  necessary,  and  soak  a  piece  of  colored  calico  (?) 
and  some  litmus  paper  in  the  filtrate.  Remove  these  articles 
to  a  beaker  containing  a  little  dilute  sulphuric  acid  (?).  Re- 
peat these  two  operations  with  the  same  litmus  and  calico,  if 
at  first  little  effect  is  seen.  What  substance  produces  the 
effect?  Why  is  the  sulphuric  acid  required  (see  55  a)? 

What  evidence  does  this  experiment  furnish  that  hypo- 
chlorous  acid  is  a  more  active  oxidizing  agent  than  is  atmos- 
pheric oxygen?  Why  is  it  thus  more  active? 

How  could  you  prepare  an  aqueous  solution  of  pure  calcium 
hypochlorite  [R  267,  268]? 

67.   Chlorates  [Hood]. 

a.  Dissolve  3  g.  (weighed  on  laboratory  scales)  of  solid 
potassium  hydroxide  in  7  c.c.  of  water  in  a  test-tube  and 
saturate  (Test?  The  solution  must  cease  to  feel  soapy)  the 
solution  with  chlorine.  While  the  saturation  is  proceeding, 
calculate  the  volume  of  chlorine  (at  0°  and  760  mm.)  required 
to  interact  with  3  g.  of  potassium  hydroxide,  one  atomic 
weight  of  chlorine  being  needed  for  each  molecule  of  potassium 
hydroxide.  At  five  bubbles  to  1  c.c.,  how  many  bubbles  of 
chlorine  will  be  used?  Observe  how  many  bubbles  issue  from 
your  apparatus  in  fifteen  seconds,  and  calculate  how  long  the 
operation  may  be  expected  to  take  (?).  Crystals  will  appear 
during  the  process  of  saturation  and  will  increase  in  quantity  as 
the  liquid  afterwards  cools.  Filter  off  the  crystals  on  a  small 
filter  paper,  and  examine  the  filtrate  and  the  crystals  (in  6) 
separately  as  follows  : 

Add  to  the  filtrate  dilute  nitric  acid  (this  is  to  destroy  potas- 
sium hydroxide,  in  case  any  remains :  no  equation  needed) ,  and 
test  with  a  few  drops  of  silver  nitrate  solution  (?).  What 
radical  is  shown  by  this  test  to  be  present  (54  a)?  What 
product  is  thus  shown  to  have  been  formed  by  the  interaction 
of  chlorine  and  potassium  hydroxide? 

6.  Examine  the  crystals  from  a  with  a  lens  and  describe 
them.  Dry  the  crystals,  heat  them  in  a  narrow  tube,  and 


§  58]  DOUBLE   DECOMPOSITION  51 

test  for  oxygen  (?).  Dissolve  the  residue  from  this  operation 
in  distilled  water  and  add  silver  nitrate  solution  (?).  What 
substances  constituted  the  crystals  and  the  residue,  respec- 
tively? From  the  behavior  of  the  former  substance  during 
making,  what  do  you  infer  as  to  its  solubility?  Is  the  infer- 
ence correct  (Appendix  IV)  ? 

What  effect  was  observed  on  adding  silver  nitrate  solution  to 
a  solution  of  potassium  chlorate  (54  a)?  How  may  the  chlo- 
rate radical  be  distinguished  from  that  of  the  chlorides?  The 
crystals  of  potassium  chlorate  made  in  a  are  not  free  from 
traces  of  potassium  chloride  (why?),  and  could  not  therefore 
be  utilized  for  this  test.  What  method'  should  you  suggest 
for  purifying  the  chlorate  [R  273]? 

To  a  minute  amount  of  finely  powdered  potassium  chlorate 
add  a  few  drops  of  pure,  concentrated  hydrochloric  acid 
(66  a)  (?).  The  yellow  substance  is  formed  by  decomposition 
of  one  of  the  products  [R  275]  (?).  How  would  a  chloride 
behave  with  hydrochloric  acid? 

Give  the  three  ways  of  distinguishing  chlorides  from  chlo- 
rates. 

68.    Perchlorates. 

a.  Measure  600  c.c.  of  water  into  your  1-liter  bottle,  and 
mark  the  level  reached.  Observe  the  temperature  and  pressure 
of  the  air  and  calculate  the  weight  of  potassium  chlorate  which 
will  be  necessary  to  give  600  c.c.  of  oxygen  under  these  conditions 
(the  tension  of  aqueous  vapor  may  be  neglected,  as  the  vapor 
will  occupy  only  about  10  c.c.  of  the  600  c.c.  at  18°)  and  at  the 
same  time  leave  the  perchlorate  and  chloride  as  a  residue. 
This  stage  is  reached  when  one-fifth  of  the  total  oxygen  has  been 
evolved :  in  other  words,  take  so  much  of  the  chlorate  as,  if 
completely  decomposed,  would  furnish  five  times  600  c.c. 

Fill  the  1-liter  bottle  with  water  and  invert  it  over  the  pneu- 
matic trough.  Weigh  the  calculated  amount  of  chlorate  into 
a  hard  glass  test-tube,  which  has  previously  been  closely  fitted 
with  a  one-hole  cork  and  delivery  tube,  and  see  that  the  appa- 
ratus has  been  made  air-tight.  Gently  heat  the  chlorate  and 
collect  in  the  1-liter  bottle  enough  oxygen  to  fill  the  bottle  to 
the  mark,  measured,  of  course,  when  the  mark  is  at  the  same 
level  as  the  water  in  the  trough.  Proceed  slowly  towards  the 
end  so  as  to  allow  the  gas  to  cool,  stop  heating  when  the  mark 
is  reached,  and  remove  the  delivery  tube  at  once  from  the 
water.  Pour  the  melted  substance  into  a  mortar  before  it  has 
time  to  solidify.  Pulverize  the  mixture. 

The  mixture  consists  mainly  of  the  chloride  and  perchlorate 


52  DOUBLE   DECOMPOSITION  [§59 

of  potassium.  The  solubilities  (grams  of  the  salt  dissolved  by 
100  c.c.  of  water)  of  these  salts  are  as  follows: 

15°          20°          100° 

Potassium  chloride 33  35  56 

Potassium  perchlorate     ...       1.5          1.8          20 

To  separate  the  substances,  calculate  approximately  the  amount 
of  potassium  chloride  which  must  be  present,  and  shake  the 
powder  persistently  with  an  amount  of  cold  water  just  suffi- 
cient to  dissolve  this  salt.  Cut,  fold,  and  place  in  a  funnel  a 
filter  paper  just  large  enough  to  hold  the  undissolved  material. 
Collect  the  latter  upon  the  filter  and  wash  it  with  a  few  drops 
of  cold  water.  Calculate  the  amount  of  water  which  at  100° 
will  dissolve  the  residue,  assuming  it  to  be  potassium  perchlo- 
rate. Dissolve  it  in  this  amount  of  water  by  boiling,  and  allow 
the  solution  to  stand  for  an  hour  or  two.  Collect  the  crystals 
upon  a  filter,  wash  them  as  before,  and  dry  them  on  a  radiator. 

6.  Dissolve  a  little  of  the  substance  in  distilled  water  and 
test  with  silver  nitrate  solution  (?).  Explain  (66  a). 

To  a  minute  amount  of  the  crystals  add  a  few  drops  of  pure 
concentrated  hydrochloric  acid  [R  276]  (?).  Why  does  the 
result  differ  from  that  when  potassium  chlorate  was  treated 
with  the  same  acid  (67  6)? 

Place  about  1  g.  of  the  crystals  in  a  narrow  test-tube,  heat, 
and  test  for  oxygen  (?). 

How  could  you  distinguish  a  perchlorate  from  a  chloride,  and 
from  a  chlorate? 

69.   Bromic  and  lodic  Acids. 

a.  Take  two  test-tubes  and  place  in  one  a  minute  fragment 
of  iodine  and  in  the  other  2-3  drops  of  bromine-water.     Add 
about  5-10  c.c.  of  water  and  a  little  carbon  disulphide  to  each, 
and  shake  (43  a  and  47  a).     The  carbon  disulphide  is  added 
simply  for  the  purpose  of  collecting  the  halogen  and  making  its 

Eresence  obvious.  Now  pass  chlorine  (generated  as  in  43  6) ,  a 
iw  bubbles  at  a  time,  through  (or  add  chlorine-water,  a  few 
drops  at  a  time,  to)  the  water  in  the  test-tubes,  alternately, 
and  shake  vigorously  after  each  addition  of  chlorine  until  a 
change  is  seen  [R  277]  (?).  Which  of  the  halogens  is  first 
affected,  and  why? 

b.  To  about  10  c.c.  of  water  in  a  test-tube  add  a  single  drop 
of  potassium  iodide  solution  and  then  a  single  drop  of  potas- 
sium bromide  solution.     Introduce  also  a  few  drops  of  carbon 
disulphide.      Now  pass  chlorine  (generated  as  in  43  6),  a  few 
bubbles  at  a  time,  into  the  liquid,  or  add  chlorine-water  a 


§60]  -  DOUBLE   DECOMPOSITION  58 

little  at  a  time,  shaking  vigorously  after  each  addition  of 
chlorine  (?).  Continue  until  no  further  changes  occur,  and 
explain  all  the  changes  which  are  observed.  This  procedure 
is  used  in  analysis  for  recognizing  a  bromide  in  presence  of  an 
iodide. 

c.  Prepare  some  dilute  bromic  acid  by  taking  2-3  c.c.  of 
potassium  bromate  solution  and  adding  an  equal  volume  of 
dilute  sulphuric  acid  (?).  Make  the  equation  for  this  double 
decomposition.  Is  the  action  complete  (55)?  In  what  fol- 
lows, disregard  the  substances  present  with  the  bromic  acid, 
and  place  the  latter  only  in  the  equation.  Drop  into  this  solu- 
tion a  single  small  crystal  of  iodine  and  shake  repeatedly, 
allowing  the  mixture  to  stand  for  some  minutes  after  each  shak- 
ing^). Pour  off  the  solution  from  any  undissolved  iodine,  and 
to  the  clear  liquid  add  a  few  drops  of  carbon  disulphide  (?). 
What  free  halogen  is  here  detected?  What  does  this  show  in 
regard  to  the  relative  tendencies  of  bromine  and  iodine  to  unite 
with  oxygen?  What  inference  can  you  draw  in  regard  to  the 
relative  activity  of  chlorine  towards  oxygen?  What  would 
be  the  action  of  iodine  upon  a  solution  of  chloric  acid? 

Which  variety  of  chemical  change  was  here  observed?  How 
could  you  show  that,  although  no  change  is  visible,  the  bromic 
acid  actually  is  formed  when  the  sulphuric  acid  is  added,  above, 
and  that  it  is  the  bromic  acid,  and  not  the  potassium  bromate, 
which  interacts  with  the  iodine? 

60.   Peroxides. 

a.  Dissolve  about  2  g.  of  sodium  peroxide  in  100  c.c.  of  cold 
water  in  a  flask.     Add  this  amount  of  the  oxide,  a  very  little  at 
a  time,  shaking  and  cooling  (why?  [R  571])  the  mixture  in  a 
stream  of  water  during  the  process.     While  still  cooling  the 
solution,  add  to  it  dilute  sulphuric  acid  a  few  drops  at  a  time 
until  the  mixture  is  acid  (test?).     What  does  the  liquid  now 
contain  (55  a)?      Divide  the  mixture  into  four  parts  and  use 
them  in  b,  c,  d,  and  e. 

b.  To  one  portion,  contained  in  a  small  test-tube,  add  finely 
powdered  manganese  dioxide   (?).     Test  the  escaping  gas  for 
oxygen.     What  role  does  the  manganese  dioxide  play  here? 

c.  Prepare  a  solution  containing  free  permanganic  acid  and 
sulphuric  acid  by  adding  a  large  excess  of  dilute  sulphuric 
acid  to  5  c.c.  of  potassium  permanganate  solution  (equation? 
See  55).     Add  some  of  this  mixture  to  the  second  portion 
(from  a).     Test  for  oxygen  the  gas  which  comes  off  (?).     What 
variety  of  chemical  activity  does  the  hydrogen  peroxide  show 
here? 

d.  To  the  third  portion  add  some  starch  emulsion  containing 


54  DOUBLE  DECOMPOSITION  [§  60 

a  drop  of  potassium  iodide  solution  (?).  In  writing  the  equa- 
tion for  this  action  remember  that  the  solution  of  hydrogen 
peroxide  from  a  contained  excess  of  sulphuric  acid,  which  will 
interact  (65)  with  the  potassium  iodide  (?).  The  product  of 
this  action  then  interacts  with  the  hydrogen  peroxide.  What 
variety  of  chemical  activity  does  the  hydrogen  peroxide  show 
here? 

e.  To  the  fourth  portion  add  5  c.c.  of  ether  (object  of  this 
[R  306]?)  and  shake,  and  then  add  one  drop  and  no  more  of 
potassium  dichromate  solution  and  shake  again  (?).  This  is 
one  of  the  most  characteristic  and  delicate  tests  for  hydrogen 
peroxide. 

State  what  substance  here  combines  with  the  hydrogen  per- 
oxide and  how  it  is  formed  [R  305-306].  Make  no  equation. 

/.  Suspend  lead  dioxide,  barium  dioxide,  and  pulverized 
manganese  dioxide,  separately,  in  water,  add  dilute  sulphuric 
acid  and  shake  for  some  time,  cooling  as  in  a.  Filter,  and  apply 
to  each  filtrate  the  test  described  in  e  (?).  What  are  the  dif- 
ferences in  behavior  and  constitution  between  a  true  peroxide 
and  those  oxides  which  are  sometimes  called  peroxides  [R  308]  ? 

g.  What  are  the  radicals  of:  Bromic  acid,  potassium  chlorate, 
hypochlorous  acid,  bleaching  powder,  sodium  peroxide,  potas- 
sium permanganate,  iodic  acid,  potassium  perchlorate? 


CHAPTER  X. 

IONIZATION   AND   INTERACTIONS   OF   ACIDS,   BASES,   AND 
SALTS. 

61.  lonization.  Name  the  four  distinct  methods  by  which 
we  may  ascertain  experimentally  whether  a  substance  is 
ionized  in  solution  or  not,  and  learn  the  extent  of  the  ioniza- 
tion  [R  289,  292,  293,  328].  Define  the  term  ionization. 

The  degrees  to  which  aqueous  solutions  of  many  substances 
are  ionized  are  given  in  Appendix  VI.  Constant  reference  to 
this  will  be  necessary  in  interpreting  the  observations  in  this  and 
succeeding  chapters. 

The  experiments  of  this  paragraph  may  be  postponed  until 
after  the  work  in  62  or  63  has  been  done,  if  a  set  of  the  appa- 
ratus is  not  available  at  this  moment. 

Obtain  [Storeroom]  a  pair  of  electrolytic  cells*  (Fig.  15)  and 


Fig.  is 

half  fill  one  with  dilute  sulphuric  acid.     When  some  material 
has  been  placed  in  the  second  cell,  and  both  cells  are  connected 

*  Each  cell  consists  of  a  glass,  flat-bottomed,  specimen  tube  (about 
75  x  22  mm.)  fitted  with  a  two-hole  rubber  stopper  in  which  a  ver- 
tical groove  has  been  cut  to  permit  the  escape  of  gases.  The  electrodes 
are  pieces  of  glass  tubing  (about  10  cm.  long)  into  which  platinum 
wires  have  been  sealed  by  means  of  sealing-glass.  Contact  is  made  by 
means  of  a  thin  copper  wire  welded  to  the  inner  end  of  the  platinum 
wire.  The  platinum  wire  projects  about  15  mm.  and  is  turned  upward 
and  stuck  to  the  outside  wall  of  its  tube  by  means  of  sealing-glass.  To 

66 


56 


ACIDS,  BASES,  AND   SALTS 


[§  61 


in  series  with  the  source  of  electricity,*  an  evolution  of  gas  in 
the  first  cell  will  indicate  that  the  circuit  is  complete  and  that, 
therefore,  the  material  which  has  been  placed  in  the  second  cell 
is  a  conductor.  If,  on  the  other  hand,  the  material  in  the  second 
cell  is  a  non-conductor,  or  even  a  very  bad  conductor,  no  evo- 
lution of  gas  will  be  observed  in  the  first  cell.  If  the  material 
in  the  second  cell  is  a  solution  and  a  conductor,  what  conclusion 
may  be  drawn  in  regard  to  the  condition  of  the  dissolved  body 
[R  326]  ? 

Half  fill  the  second  cell  with  the  substances  named  below  in 
turn.  See  very  particularly  that  the  electrodes  in  each  cell  are 
not  touching  one  another.  Connect  with  the  battery,  and  ob- 
serve the  effect  in  the  first  cell.  When  the  same  experiment 
has  been  shown  in  the  class-room,  the  result  may  be  recorded 
here  and  the  experiment  omitted.  Wash  the  second  cell  and 
electrodes  very  carefully  after  each  trial. 

The  following  eight  substances,  or  solutions,  show  the  behavior 
typical  of  the  classes  of  materials  to  which  each  example  belongs. 
After  giving  the  result  in  your  notes,  name  the  class  which  is 
illustrated  in  each  case. 


Fig.  16 

secure  a  large  electrolytic  surface,  the  tubes  are  dipped  for  a  distance 
of  20  mm.  in  strong  chloroplatinic  acid  solution  and  heated  in  the 
Bunsen  flame.  This  leaves  a  coating  of  metallic  platinum  on  their 
surface. 

The  cells  are  set  into  holes  bored  in  a  small  block  of  wood.  To 
protect  the  latter  from  the  action  of  acids  the  blocks  should  be  prepared 
by  soaking  in  hot  paraffin. 

*  A  storage  battery  of  three  cells  in  series  may  be  used,  but  is 
always  in  danger  of  being  ruined  by  short-circuiting  through  careless- 
ness. Protection  by  means  of  a  fuse  leads  to  continual  interruptions 
of  the  work.  The  best  plan  is  to  use  the  current  passing  from  the 
lighting  circuit  (D,  Fig.  16),  through  two  100-candle-power  lamps  (or 
an  equivalent  arrangement  of  other  lamps),  one  on  each  wire  from  the 
dynamo,  and  to  reduce  the  voltage  to  6-8  volts  by  means  of  a  suitable 
shunt  (S).  With  a  lamp  on  only  one  wire,  there  is  danger  that  a  student 
may  produce  a  short  circuit  by  allowing  the  other  wire  to  touch  a  gas 
connection  or  steam  pipe. 


§  62]  ACIDS,  BASES,  AND   SALTS  67 

a.   Dry,  crystallized  sodium  chloride  (?). 
6.   Distilled  water  (?). 

c.  Aqueous  solution  of  sodium  chloride  [Side-shelf]  (?). 

d.  Diluted  aqueous  solution  of  sodium  hydroxide  [Desk]  (?). 

e.  Diluted  aqueous  solution  of  hydrogen  chloride  [Desk]  (?). 
/.   Aqueous  solution  of  sugar  (?).     Dry  the  cell  by  washing 

first  with  alcohol  and  then  with  ether. 

g.   Toluene  in  the  dried  cell  (?). 

h.  Hydrogen  chloride  dissolved  in  dry  toluene  [Side-shelf]  (?). 
What  difference  between  water  and  toluene  do  e  and  h  bring  to 
light?  Keep  this  solution  corked  up  in  a  dry  test-tube  for  use 
in  65  d. 

62.  Ionic  Materials.  The  chemical  composition  of  the  ions 
into  which  any  compound  is  divided  by  solution  in  water  may 
be  ascertained  in  two  ways:  (1)  by  electrolysis  and  examina- 
tion of  the  substances  liberated  at  the  electrodes  [R  310-312], 
and  (2)  by  studying  the  interactions  (particularly  the  double 
decompositions,  64)  of  the  substance  with  other  substances 
[R  281-283],  for  the  radicals  and  ions  of  a  substance  are  the 
same.  What  classes  of  chemical  compounds  are  alone  ionized? 

The  ionic  substances  may  be  named  as  follows: 

Substance.  Name. 

Ionic  sodium  (Na*)  Sodium-ion. 

Ionic  hydrogen  (H*)  Hydrogen-ion. 

Ionic  chlorine  (Cl')  Chloride-ion. 

Ionic  chlorate  radical  (CKV)  Chlorate-ion. 

Ionic  hydroxyl  (OH')  Hydroxide-ion. 

Ionic  ferric  iron  (Fe"')  Ferric-ion. 

Ionic  ferrous  iron  (Fe")  Ferrous-ion. 

Ionic  bisulphate  radical  (HSO/)    Hydrogen-sulphate-ion. 

In  using  these  terms,  note  that  sodium-ion  (with  the  hyphen) 
is  the  name  of  the  substance,  and  not  of  the  hypothetical, 
charged  atom.  When  speaking  in  terms  of  hypothesis,  there- 
fore, we  may  not  say  "a  sodium-ion,"  or  "sodium-ions,"  any 
more  than  we  should  say  "an  ionic  sodium"  or  "ionic  sodiums." 
To  describe  the  charged  atom  or  group  of  atoms,  we  must  write 
"a  sodium  ion,"  "sodium  ions,"  "chlorate  ions,"  etc. 

In  accordance  with  the  above  nomenclature,  give  the  names 
and  symbols  (not  forgetting  the  charges)  of  the  three  chief 
physical  components,  i.e.,  distinct  substances  (in  addition  to 
water),  present  in  the  aqueous  solutions  of  sodium  chloride, 
hydrogen  chloride,  and  sodium  hydroxide  [R  334]  (?).  In 


68  ACIDS,  BASES,  AND   SALTS  [§  63 

these  solutions  there  are  still  other  physical  components  pres-. 
ent  in  small  amounts  —  which  are  these  in  each  of  the  cases 
just  mentioned  [R  344]?  Give  a  concise  comparative  state- 
ment of  the  specific  physical  properties  (such  as,  color,  molec- 
ular weight,  solubility,  behavior  towards  electrically  charged 
bodies,  physical  state)  of  the  ionic  and  the  free  forms  of  sodium, 
hydrogen,  and  chlorine  (?). 

63.  Relations  of  the  Molecular  Substance  to  its  Constit- 
uent Ionic  Substances  (in  Equilibrium).  The  ions  of  an  ion- 
ogen  and  the  remaining  molecules  are  in  chemical  equilibrium 
[R  297].  What  changes  take  place,  respectively,  when  the 
solution  is  concentrated  by  evaporation  and  when  it  is  diluted, 
as  in  a,  below  [R  297-298,  335]  ?  Can  the  proportion  of  mole- 
cules be  increased  otherwise  than  by  concentrating  the  solu- 
tion (see  6,  below)  [R  335-336]  ?  With  substances  like  sodium 
chloride  and  hydrogen  chloride  these  changes  cannot  be  per- 
ceived by  the  eye  (why?).  In  the  following  instances  (a  and 
b)  the  ionic  and  molecular  substances  are  both  perceptible  to 
the  eye,  and  their  relations  as  described  above  may,  therefore, 
be  studied  very  easily. 

a.  Examine  a  solution  of  potassium  bromide.     What  is  the 
color  of  bromide-ion?    Take  a  minute  amount  (say  0.2  g.)  of 
cupric  bromide  in  a  dry  test-tube.     Add  two  drops  of  water  and 
agitate  for  some  time  (?).     Then  add  more  water,  a  drop  or 
two  at  a  time,  agitating  vigorously,  and  giving  the  substance 
time  to  dissolve,  if  it  can,  after  each  addition.     Continue  the 
addition  of  water  cautiously  until  the  substance  has  all  dis- 
solved, and  afterward  until  the  change  in  color  is  complete, 
and  then  stop.     What  is  the  color  of  the  molecules  of  cupric 
bromide?    What   is    the    color    of   cupric-ion?     Compare    the 
color   with  that  of   cupric    sulphate  solution  (?)    and   explain. 
Formulate  the  change  which  has  been  witnessed. 

b.  Now  take  a  fresh  portion  of  cupric  bromide  and  repeat 
the  experiment  as  in  a,  stopping  the  addition  of  water  at  the 
green  stage.     Divide  the  mixture  into  two  parts.     To  one  add 
2-3  g.  of  solid  potassium  bromide  and  shake  vigorously  (?). 
To  the  other  portion  add  4-5  g.  of  solid  cupric  chloride  (?). 
Interpret  the  results. 

The  converse  case,  in  which  one  of  the  ions  is  removed  and 
the  dissociation  is  promoted,  is  discussed  in  d. 

c.  Many  ionic   substances  are   colored,   although  the   color 
does  not  always  differ  markedly  from  that  of  the  molecules. 
Examine  the  following  solutions  [Side-shelf],  make  a  list  of  the 
ionic  substances  contained  in  them,  with  their  formulae  and 
charges,  and  note  the  color  of  each  kind  of  ions :  cobalt  chloride, 


§  64]  ACIDS,  BASES,  AND   SALTS  59 

potassium  permanganate,  potassium  dichromate,  chrome-alum 
(this  last  solution  freshly  made  by  dissolving  the  solid). 

d.  Just  as  the  union  of  ions  to  form  molecules  may  be  pro- 
moted by  addition  of  a  substance  yielding  a  common  ion  (? 
63  b),  so  the  reverse  of  this,  namely,  the  dissociation  of  mole- 
cules into  ions,  may  be  promoted  by  the  removal  of  one  of  the 
ionic  materials.  The  removal  of  ions  may  be  accomplished  in 
several  ways  [R  360-364]: 

(1)  By  union  of  the  ion  with  some  other  ion,  when  the  mole- 
cules thus  formed  are  insoluble.    This  case  will  be  illustrated 
next  (see  64). 

(2)  By  union  of  the  ion  with  some  other  ion,  when  the  mole- 
cules thus  formed,  although  soluble,  are  very  little  dissociated 
by  water  (see  66,  75,  and  92  a). 

(3)  By  discharge  of  the  ion  and  liberation  of  its  material, 
through  transfer  of  the  charge  to  another  substance  (see  68). 

(4)  By  union  of  the  ion  with  some  other  material  to  form  a 
compound  ion,  illustrated  in  54  b. 

(5)  By  decomposition  of  the  ion,  as  in  59  c. 

(6)  By  the  mere  change  in  the  valence  (amount  of  the  charge) 
of  an  ion,  for  this  converts  it  into  another  substance  of  the 
same  material  composition  (see  160  g,  167  b,  168  d). 

(7)  By  discharge  of  the  ion  and  liberation  of  its  material 
through  electrolysis.     This  was  illustrated  in  61. 

64.   Precipitation  on  Mixing  lonogens. 

a.  Place  3-4  c.c.  of  silver  nitrate  solution  in  a  test-tube 
and  dilute  with  water.  Add  potassium  chloride  solution 
cautiously  and  agitate  continuously,  until  no  further  precipi- 
tation occurs  (?).  Filter,  concentrate  the  filtrate  by  evapora- 
tion, and  pour  it  into  a  watch-glass  to  crystallize  (?).  Two 
salts  are  formed. 

Formulate  the  action   (Fig.   17).     In  doing  this,  show  the 

K-    +C1' 


Tl       U 

(dsolvd.)  KNO3     AgCl  (dsolvd.) 

U 

AgCl  (solid) 
Fig.  17 

three  main  physical  components  of  each  of  the  original  solu- 
tions and  the  relations  of  these  components  (in  equilibrium)  to 
one  another  in  each  case.  Show  also  the  molecular  products 


60  ACIDS,  BASES,  AND  SALTS  [§  65 

formed  when  the  solutions  are  mixed.  Assuming  that  the 
solutions  are  approximately  normal  [R  148],  ascertain  the 
proportions  in  which  the  original  components  are  present 
before  mixing  (Appendix  VI).  Learn  also  to  what  extent  the 
molecular  products  will  be  formed  by  union  of  the  ions  (Appen- 
dix VI),  and,  in  the  case  of  an  insoluble  substance,  how  com- 
plete will  be  the  precipitation  (Appendix  IV).  On  the  basis 
of  this  complete  information,  explain  in  detail,  and  one  by  one, 
in  what  way,  and  to  what  extent,  each  of  the  six  original  com- 
ponents is  affected  by  the  results  of  mixing. 

Name  the  components  of  the  filtrate  and  explain  how  each 
is  affected  by  the  evaporation  and  crystallization. 

How  does  the  formation  of  the  precipitate  of  silver  chloride 
illustrate  63  d  (1)?  Upon  what  factor  does  the  completeness 
of  the  change  depend?  Is,  or  is  not,  silver  chloride  a  highly 
ionized  substance  [R  332]  ? 

Aside  from  double  decompositions,  what  means  have  we  for 
learning  of  what  radicals  a  salt  (like  silver  nitrate)  is  composed? 

6.  To  a  little  cupric  sulphate  solution  in  a  test-tube  add 
sodium  hydroxide  solution  (?).  Exactly  as  in  64  a  (second 
par.),  formulate,  study  and  explain  the  whole  action.  How 
does  this  illustrate  (1)  of  63  d  ? 

To  what  classes  of  ionogens  do  the  four  molecular  substances 
respectively  belong? 

c.  To  a  little  cupric  sulphate  solution  add  a  little  dilute 
hydrochloric  acid  (?).  In  what  respects  does  the  result  differ 
from  those  in  a  and  b,  and  why?  Can  any  acids  be  prepared 
by  precipitation,  and  if  so,  which?  Give  illustrations. 

65.  Bases  and  Acids:  Hydroxide-ion  and  Hydrogen-ion: 
Indicators. 

a.  Examine  distilled  water  in  respect  to  (a)  taste,  (b)  be- 
havior with  litmus,  (c)  conductivity  (done  already,  61  6). 

6.  Dissolve  a  small  piece  of  sodium  hydroxide  in  water  and 
examine  the  solution  in  respect  to  (a)  taste,  by  diluting  a 
little  and  tasting  one  drop,  (b)  behavior  with  litmus,  (c)  be- 
havior with  phenolphthalem,  (d)  conductivity  (see  61  d). 
These  properties  belong  to  aqueous  solutions  of  all  bases. 
Aside  from  the  water,  what  component  alone  is  common  to  all 
such  solutions  and  has  the  above  properties? 

c.  Examine  an  aqueous  solution  of  hydrochloric  acid  in 
respect  to  (a)  taste,  (b)  behavior  toward  litmus,  (c)  behavior 
with  phenolphthalem,  (d)  conductivity  (see  61  e),  (e)  action 
on  a  piece  of  marble,  (f)  action  on  an  iron  nail  (clean  this  with 
the  file  before  use).  These  properties  are  shown  by  all  aqueous 
solutions  of  acids.  Aside  from  the  water,  what  component 


§  66]  ACIDS,  BASES,  AND  SALTS  61 

alone  is  common  to  all  such  solutions  and  has  these  proper- 
ties ? 

d.  Take  the  solution  of  hydrogen  chloride  in  toluene  (61  H) 
and  examine  it  in  respect  to  (a)  conductivity  (see  61  h),  (b) 
action  on  a  piece  of  marble,  dried  in  advance  by  heating  in  a 
dry  porcelain  dish  for  a  few  moments,  (c)  action  on  an  iron 
nail  (clean  as  before).  Be  sure  that  perfectly  dry  vessels  are 
used  in  these  experiments.  What  substance  identified  in  c  is 
absent  from  this  solution?  What  difference  between  water 
and  toluene,  as  solvents,  does  this  result  indicate?  In  what 
three  other  respects  would  the  two  solutions  of  hydrogen  chlo- 
ride be  found  to  differ? 

66.  Ionic  Chemical  Changes:  I.  Union  and  Disunion  of 
Ions:  Neutralization  (Union  of  H*  and  OH').  (Two  students 
working  together.)  A  considerable  chemical  change  may  occur 
not  only  in  precipitation  (see  64),  but  also  when  ions  unite  to 
form  a  substance  which,  although  soluble,  is  very  little  ionized 
by  water.  Such  changes  are  illustrated  in  66  and  67. 

Weigh  out  5  g.  (laboratory  scales)  of  potassium  hydroxide, 
dissolve  it  in  50  c.c.  of  distilled  water,  and  pour  the  clear  solu- 
tion into  a  burette  (Fig.  2,  p.  7).  Measure  10  c.c.  of  con- 
centrated hydrochloric  acid  in  the  graduated  cylinder,  mix  it 
in  a  small  beaker  with  50  c.c.  of  distilled  water,  and  pour  this 
into  a  second  burette.  Now,  into  a  small  beaker  or  flask  run 
15  c.c.  of  the  acid  solution  from  the  second  burette,  and  then 
add  to  it  two  drops  of  phenolphthalein  solution.  Place  the 
vessel  under  the  first  burette,  read  the  level  of  the  liquid  in 
the  burette,  and  allow  the  alkali  to  run  into  the  acid  drop  by 
drop,  stirring  constantly,  until  the  last  drop  confers  the  faintest 
perceptible  pink  tinge  on  the  whole  solution.  If  you  do  not  at 
first  succeed  in  stopping  at  the  right  point,  repeat  the  experi- 
ment. Note  the  volume  of  alkali  used.  Concentrate  the  solu- 
tion on  the  sand  bath  until  a  drop  deposits  crystals  on  cooling, 
and  then  remove  the  dish  from  the  sand  bath  promptly  and 
set  it  aside. 

When  sufficient  crystals  have  appeared,  dry  them  with  filter 
paper  and  examine  with  respect  to  (a)  form,  (b)  taste,  (c) 
exposure  to  moist  air,  (d)  action  of  a  solution  on  litmus,  (e) 
conductivity  of  aqueous  solution  (done  already,  61  c).  Con- 
struct a  table  comparing  the  substance  in  these  respects  with 
the  materials  from  which  it  was  made.  Compare  the  substance 
with  potassium  chloride  on  the  side-shelf.  How  should  you 
determine  whether  a  substance  obtained  in  this  way  contained 
"water  of  crystallization"  or  not?  Make  the  necessary  experi- 
ments (?).  Wash  out  the  burettes. 


62  ACIDS,  BASES,  AND   SALTS  [§  67 

Following  the  directions  in  64  a  (second  par.),  formulate, 
study,  and  explain  the  whole  action.  Note,  however,  that 
there  is  here  no  insoluble  substance.  Show  how  this  experi- 
ment illustrates  63  d  (2). 

Express  the  change  involved  in  every  neutralization  of  highly 
ionized  substances  by  means  of  the  simplest  equation.  How 
may  neutralization  be  defined,  in  terms  of  the  hypothesis  of 
ions?  How  may  it  be  denned,  taking  account  of  all  the  facts, 
but  omitting  all  reference  to  ions 

Calculate  the  approximate  concentration,  in  terms  of  a  nor- 
mal solution  as  unity,  of  the  potassium  hydroxide  solution 
used  above  (?).  From  the  volumes  of  alkali  and  acid  used  in 
neutralizing,  calculate  the  concentrations  of  the  diluted  hydro- 
chloric acid,  and  of  the  concentrated  acid  employed  to  make 
it,  expressing  the  concentrations  in  terms  of  a  normal  solution. 
Calculate  the  number  of  grams  of  hydrogen  chloride  per  liter  in 
the  dilute  and  concentrated  acids,  respectively. 

67.  Neutralization  of  Slightly  Ionized  and  of  Insoluble 
Substances. 

a.  Consider  the  degree  of  ionization  of  acetic  acid  (Appendix 
VI).     To  neutralize  1  liter  of  normal  acetic  acid,  would  more 
or  less  alkali  be  required  than  to  neutralize  1  liter  of  normal 
hydrochloric  acid?    In  what  way,  precisely,  would  the  details 
of  the  change  be  different  in  the  case  of  acetic  acid  [R  356]? 
Name  some  of  the  consequences  of  this  difference  [R  357-358]. 

b.  Dilute  a  few  drops  of  cupric  sulphate  solution  with  water 
and  add  excess  of  sodium  hydroxide  solution  (?).     Fit  a  filter 
paper  properly  into  a  funnel  (Fig.  3,  p.  9).      Filter  the  mix- 
ture, and   wash  the  precipitate    (?)   repeatedly  with  distilled 
water  to  remove  soluble  substances.     Now  place  a  clean  test- 
tube  below  the  funnel,  perforate  the  bottom  of  the  filter  paper, 
and  wash  the  precipitate  through  into  the  test-tube  by  means 
of  a  stream  of  water  from  the  wash-bottle.     To  the  suspended 
cupric  hydroxide,  cautiously  add  dilute  hydrochloric  acid  in 
amount  just  sufficient  to  give  a  clear  liquid.     Concentrate  the 
liquid  on  the  sand  bath  until  a  drop,  removed  to  a  watch-glass, 
shows  signs  of  crystallizing  when  cold.     Then  remove  the  dish 
promptly  from  the  sand  bath  and  allow  it  to  cool.     Examine 
the  crystals  (?). 

Formulate  this  action  as  in  64  a,  taking  account,  however, 
of  the  fact  that  one  of  the  interacting  substances  is  an  "insol- 
uble" solid  [R  349].  Describe  in  detail  the  stages  through 
which  the  final  production  of  solid  cupric  chloride  is  accom- 
plished. 

To  what  class  of  ionic  chemical  changes  [R  360]  does  the 


§  68]  ACIDS,  BASES,  AND   SALTS  63 

foregoing  action  belong?    Answer  the  same  question  in  regard 
to  the  precipitations  of  salts  in  64. 

68.  Ionic  Chemical  Changes:  II.   Displacement. 

a.  Place  several  pieces  of  granulated  zinc  in  a  dilute  solution 
of  cupric  sulphate  and  set  aside  until  the  change  is  complete 
(test?).  Occasional  agitation  will  hasten  the  change  (why?). 
Filter.  What  is  the  precipitate  [R  361]?  Before  examining 
the  filtrate,  take  a  few  drops  of  cupric  sulphate  solution  and  a 
like  amount  of  zinc  sulphate  solution  in  two  test-tubes.  Dilute 
each  solution  with  water,  and  add  to  each  ammonium  sulphide 
solution  (?).  'What  is  the  precipitate  in  each  case,  and  what 
ions  are  required  to  form  it? 

To  the  filtrate  from  the  first  part  of  this  experiment  add 
ammonium  sulphide  solution  (?).  What  ions  were  present  in 
the  filtrate?  What  changes  did  the  zinc  and  the  cupric  ions, 
respectively,  undergo  in  the  first  part  of  the  experiment?  For- 
mulate this  change  in  an  equation.  In  the  course  of  this  ex- 
periment, what  becomes  of  the  molecular  cupric  sulphate 
(63d  (3))? 

What  substances  could  have  been  substituted  for  the  cupric 
sulphate  without  affecting  the  result?  What  substances,  be- 
side zinc,  would  have  precipitated  copper  (Appendix  VII)  ? 
What  other  elements,  beside  copper,  are  displaced  by  zinc? 

Which  of  the  elements  displaced  by  zinc  did  we  prepare  in 
quantity  by  an  action  like  the  present  (18).  Formulate  this 
action  in  terms  of  the  hypothesis  of  ions.  What  were  the 
products  of  the  action  of  zinc  upon  concentrated  sulphuric 
acid  (16  d)1  What  is  the  chief  component  of  this  form  of 
the  acid  (Appendix  VI)  ?  If  this  component  interacted  with 
the  zinc,  to  what  class  of  chemical  changes  did  this  action 
belong? 

6.  Formulate  the  actions  in  16  a  in  terms  of  the  hypothesis 
of  ions.  Explain  in  terms  of  the  hypothesis  the  differences  in 
activity  of  the  various  metals  [R  362]. 

c.  Examine  your  notes  on  Chap.  VIII.  Formulate  the  fol- 
lowing actions  in  terms  of  the  hypothesis  of  ions : 

Free  chlorine  and  bromide-ion  (43  b  and  45  g). 
Free  chlorine  and  iodide-ion  (47  c  and  50  a). 
Free  bromine  and  iodide-ion  (47  d) 
Free  iodine  and  sulphide-ion  (49). 

Arrange  these  four  elements  in  a  series  similar  to  the  electro- 
motive series  of  the  metals  (Appendix  VII).  Where  should 
you  place  fluorine  in  this  series  [R  241]  ?  Can  you  indicate  the 
approximate  position  of  oxygen  [R  239,  241]? 


64  ACIDS,  BASES,  AND    SALTS  [§  69 

69.  Ionic   Chemical  Changes:  III,  IV,   V.     In  addition  to 
union  or  disunion  of  ions  (I),  and  displacement  (II),  there  are 
three  other  ways  in  which  ions  may  undergo  chemical  change. 

One  of  these  (III)  was  illustrated  in  29  a  and  b,  in  54  b,  in 
67  a  and  b,  in  69  a,  b,  and  c,  and  in  60  c  (?). 

Another  (IV)  was  illustrated  in  29  a  (?). 

Still  another  (V)  was  illustrated  in  61  (?). 

Define  each  of  these  three  classes  of  ionic  chemical  change 
and  formulate  the  illustrations  anew  so  as  to  show  how  the 
actions  cited  belong  to  the  class  illustrated. 

Re-examine  the  seven  ways  in  which  ionic  substances  are 
removed,  and  dissociation  of  the  parent  molecules  is  promoted 
(63  d),  and  indicate  that  one  of  the  five  classes  of  ionic  change 
to  which  each  of  the  seven  belongs. 

70.  Non-Ionic    Actions.     In   previous    class-room   and   lab- 
oratory experiments  we  have  observed  the  formation  of  iono- 
gens  in  other  ways  than  those  illustrated  in  this  chapter.     These 
ways  are  non-ionic,  or  not  distinctly  ionic.     Give  illustrations 
of  such  of  these  ways  as  you  recall :  acids,  two  ways ;  bases,  one 
way;  salts,  four  ways,  together  with  the  reference  numbers  of 
the  laboratory  experiments  in  which  they  occur. 


CHAPTER  XL 

SULPHUR. 

71.  Sulphur. 

a.  In  a  dry  test-tube  place  a  very  small  piece  of  roll  sulphur 
with  2-3  c.c.  of  carbon  disulphide,  and  shake  (?).     Allow  the 
clear  solution  to  evaporate  spontaneously  (i.e.,  without  the  aid 
of  heat)  in  a  watch-glass  [Hood],  and  describe  the  crystals 
[R  138]  (?).     See  Note  25,  p.  10. 

b.  In  a  dry  test-tube  place  about  5  g.  of  roll  sulphur,  melt 
the  substance  with  the  least  possible  application  of  heat  (the 
material  must  remain  pale-yellow),  and  pour  the  melt  into  a 
beaker  of  cold  water.     Dry  some  of  the  product  with  filter 
paper  and  test  its  solubility  in  carbon  disulphide  as  in  a. 

c.  Melt  about  10  g.  of  sulphur  in  the  same  test-tube,  and  heat 
the   body  until  it   boils  (?).     Note  the    changes  in  color  and 
fluidity  that   occur.     To  learn   the   nature   of  the   substance 
formed  by  heating,  chill  the  sulphur  while  it  is  boiling  vigor- 
ously by  pouring  it  suddenly  into  cold  water  (?).     Note  the 
physical  state  of  the  product,  dry  a  part  with  filter  paper,  and 
examine  its  solubility  in  carbon  disulphide   (?).     Set  the  re- 
mainder aside  for  a  few  days,  and  then  study  its  appearance 
and  solubility  again  (?).     Keep  also  the  test-tube  from  which 
it  was  poured,  and  examine,  at  the  same  time,  in  both'  these 
respects,  the  sulphur  which  remained  adhering  to  its  walls  and 
was  not  cooled  so  suddenly  (?).     Account  for  the  change  when 
sulphur  is  heated,  and  the  differing  results  of  rapid  and  slow 
cooling  [R  369]. 

Why  are  we  convinced  that  none  of  the  changes  was  due  to 
interaction  with  the  water? 

d.  Mix  in  a  mortar  2  g.  of  iron  filings  and  1  g.  of  powdered 
sulphur.     Transfer  to  a   dry  test-tube   and  heat   gently   (?). 
When  cool,  break  the  test-tube  in  a  mortar  and  use  the  black 
product  (?)  in  72  a. 

Recall  and  record  here  a  case  of  the  union  of  sulphur  with  a 
metal  which  was  obseryed  previously. 

72.  Hydrogen  Sulphide  [Hood]. 

a.  Place  a  part  of  the  product  from  71  d,  or  about  1  g.  of 
ferrous  sulphide,  in  a  test-tube  and  add  a  little  dilute  hydro- 
chloric acid  (?).  Note  the  odor  of  the  gas,  and  apply  to  it  a 
strip  of  filter  paper  dipped  in  lead  nitrate  solution  [R  705]  (?). 

6.  With  a  Kipp's  apparatus  generating  hydrogen  sulphide, 

65 


66  SULPHUR  [§  73 

or  with  the  laboratory  supply  of  the  gas,  connect  a  glass  nozzle. 
When  the  air  has  been  displaced,  set  fire  to  the  gas.  Describe 
the  color  of  the  flame.  Hold  a  porcelain  dish  in  the  middle  of 
the  flame  for  a  few  moments  (?).  What  substance  is  depos- 
ited, and  must,  therefore,  exist  uncombined  in  the  interior  of 
the  flame?  What  other  substance  does  this  justify  us  in 
assuming  to  be  liberated  in  the  same  region?  What  do  these 
facts  indicate  regarding  the  stability  of  the  gas  when  heated, 
and  the  difficulty,  therefore,  of  making  the  compound  by  the 
direct  union  of  its  elements?  What  are  the  products  of  the 
complete  combustion  of  the  gas,  and  in  what  two  stages  does 
this  combustion  take  place?  Make  equations  showing  both 
stages. 

73.   Properties  of  Aqueous  Hydrogen  Sulphide :  I  [Hood]. 

a.  Take  about  15  c.c.  of  water  in  a  carefully  cleaned  test- 
tube  and  saturate  (test?  Note  36,  below)  it  with  hydrogen 
sulphide.  Test  the  solution  with  litmus  paper  [R  347]  (?). 
Pour  one-third  or  less  of  the  solution  into  another  test-tube 
and  boil  this  portion  vigorously,  noting  from  time  to  time  the 
odor  of  the  vapor.  Can  this  gas  be  driven  off  completely  by 
boiling?  Does  hydrogen  chloride  solution  behave  in  the  same 
way  or  differently  [R  182]  ? 

6.  Divide  the  remainder  of  the  solution  into  two  parts  and 
add  2-3  g.  of  iron  dust  (pulverized  iron)  to  one  of  them.  Shake 
vigorously  and  then  allow  the  mixture  to  stand  (?).  After  a 
few  minutes  collect  the  insoluble  matter  upon  a  filter  and  wash 
until  it  no  longer  smells  of  hydrogen  sulphide.  Transfer  the 
precipitate  to  a  test-tube  by  puncturing  the  paper  and  washing 
through.  Add  dilute  hydrochloric  acid  to  the  product  and 
note  the  odor  (?).  What  substance  must  have  been  present 
in  the  precipitate,  and  how  was  it  formed?  Account  for  the 
extreme  slowness  of  the  action  of  iron  upon  the  solution  of 
hydrogen  sulphide  [R  374]. 

c.  Allow  the  third  portion  of  the  solution  made  in  a  to  stand 
for  some  days  exposed  to  the  air  (?).     Explain  the  turbidity. 

d.  If  49  was  performed,  record  here  the  action  which  took 
place.     If  49  was  not  performed,   place   a   single   crystal   of 
iodine  in  5  c.c.  of  water  and  saturate  (test?  Note  36,  below)  the 
liquid  with  hydrogen  sulphide  [R  238]  (?). 

What  ionic  substance  is  shown  by  the  first  part  of  73  a  and 
by  73  b  to  be  present  in  the  solution  of  hydrogen  sulphide 
[R  374]  ?  Explain  the  actions  in  c  and  d  in  accordance  with 
the  hypothesis  of  ions. 

e.  To  2-3  c.c.  of  potassium  dichromate  solution  add  dilute 
sulphuric   acid  in  large   excess    (?).    What   change  may  be 


§  74]  SULPHUR  67 

assumed  to  have  taken  place?  Now  saturate  (test?  Note  36, 
below)  the  mixture  with  hydrogen  sulphide  (?).  What  are  the 
colors  of  the  solution  and  of  the  precipitate,  respectively? 
Show  that  two  kinds  of  ionic  chemical  change  are  here  illus- 
trated. 

/.  Take  2-3  c.c.  of  potassium  permanganate  solution  and 
treat  exactly  as  in  e  (?).  Answer  the  same  questions  (?). 
What  chemical  property  of  hydrogen  sulphide  is  illustrated  in 
e  and  /  ? 

Note  36.  —  To  learn  whether  a  liquid  is  saturated  with  a  gas, 
withdraw  the  delivery  tube  while  the  gas  is  issuing,  cover  the 
mouth  of  the  vessel  quickly  with  the  thumb  or  the  palm  of  the 
hand  in  such  a  way  that  the  gas  above  the  liquid  has  no  time  to 
escape  (why?),  and  shake  vigorously.  If  the  thumb  now  adheres 
to  the  mouth  of  the  vessel,  the  liquid  is  not  yet  saturated  (why?). 
If  the  liquid  is  saturated,  what  will  be  the  pressure  of  the  gas  over 
it  after  shaking  [R  153]  ?  If  air  is  allowed  to  displace  the  gas  over 
the  saturated  liquid,  what  effect  will  be  observed  on  shaking  as 
described  above? 

74.  Properties  of  Aqueous  Hydrogen  Sulphide:  II.  Sul- 
phides [Hood]. 

.  a.  What  was  the  reaction  of  aqueous  hydrogen  sulphide 
towards  litmus  (73  a)  ?  What  ionic  substances  are  present? 

b.  Take    about   6   c.c.    of   sodium   hydroxide   solution   and 
saturate  (test?  Note  36)  it  with  hydrogen  sulphide  (?).     Test 
with  litmus  (?)  and  use  in  c,  d,  e,  and  /.     How  should  you 
proceed  to  prepare  normal  sodium  sulphide  (solid)? 

c.  To  a  few  drops  of  the  solution  prepared  in  6  add  dilute 
hydrochloric  acid  (?)  (see  75  6). 

d.  To  a  few  drops  add  some  bromine-water  (?). 

e.  To  a  larger  portion  of  the  same  solution  add  a  little  pow- 
dered roll  sulphur  and  shake  from  time  to  time.     Is  sulphur 
soluble  in  water?    What  is  here  to  be  inferred  [Note  35,  p.  48]  ? 
When  the  solution  has  become  very  yellow  (?)  in  color,  filter. 
Acidify  the   filtrate  with  dilute  hydrochloric  acid    (i.e.,   add 
more  than  an  equivalent  amount  of  the  acid)   (?).     Recall  an 
experiment  with  iodine  which  resembles  this  experiment  with 
sulphur  (?). 

/.  Allow  the  remainder  of  the  solution  from  b  to  remain 
exposed  to  the  air  for  several  days  (?).  When  a  change  in 
color  has  occurred,  add  dilute  hydrochloric  acid  in  excess  (?). 
Explain. 

g.  Take  five  clean  test-tubes  and  obtain  2-3  c.c.  of  the  solu- 
tion of  each  of  the  following  substances.  Dilute  each  specimen 
with  10-20  c.c.  of  water  and  saturate  (test?)  with  hydrogen 


68  SULPHUR  [§  75 

sulphide:  (a)  Cupric  sulphate  (?),  (b)  Lead  nitrate  (?),  (c)  Cad- 
mium sulphate  (?),  (d)  Zinc  acetate  (?),  (e)  Ferrous  sulphate 
(make  a  solution  of  ferrous-ammonium  sulphate  [R  754]  and 
use  it  for  this  [Note  37,  below]). 

Explain  the  precipitation  in  accordance  with  the  hypothe- 
sis of  ions. 

Pour  away  a  part  of  the  contents  of  each  test-tube,  add  a 
large  excess  of  dilute  hydrochloric  acid,  and  shake  (?).  Explain 
the  results.  Divide  the  metallic  sulphides  obtained  in  this 
experiment  into  two  classes,  and  characterize  those  classes. 

What  property  of  hydrogen  sulphide  has  been  illustrated  in 
a,  b,  and  g  ? 

Note  37.  —  Ferrous-ammonium  sulphate  [R  754]  is  preferred  to 
ferrous  sulphate  because  it  becomes  less  rapidly  impure  through 
oxidation  by  the  air.  In  making  equations,  disregard  the  ammo- 
nium sulphate. 

75.  Ionic    Chemical    Changes:    Formation    of    an    Inactive 
Acid. 

a.  To  2-3  c.c.  of  sodium  acetate  solution  add  an  equivalent 
amount  of  dilute  sulphuric  acid,  and  warm  gently.     One  product 
may  be  recognized  by  its  odor  (?). 

Formulate,  study  and  explain  this  action  according  to  the 
directions  in  64  a  (second  par.).  Write  a  simple  equation  ex- 
pressing the  chief  change  which  occurs. 

b.  Consider  the  action  between  sodium-hydrogen  sulphide 
and  hydrochloric  acid  in  74  c.     Formulate,  study  and  explain 
this  action  as  in  64  a  (second  par.),  modifying  the  scheme  of 
formulation  to  suit  the  case.     Does  the  escape  of  the  hydrogen 
sulphide  assist  materially  in  making  the  action  more  nearly 
complete?    Does  it   assist   at   all?    What   property  does  the 
escape  of  the  hydrogen  sulphide  as  a  gas  show  this  substance 
to  possess? 

c.  Make  a  single  general  statement  describing  all  the  cases 
in  which,  when  ionogens  are  mixed,  and  no  precipitation  or 
volatilization  occurs,  a  fairly  complete  chemical  change  will 
nevertheless  take  place  (see  66). 

Give  a  list  of  acids  (Appendix  VI)  which  might  be  formed 
in  accordance  with  the  principle  embodied  in  your  statement. 

Could  any  bases  be  formed  in  accordance  with  the  same 
principle?  Illustrate  (Appendix  VI).  Could  any  salts  be  so 
formed  (Appendix  VI)  ? 

76.  Hydrolysis. 

a.  Dissolve  a  single  crystal  of  sodium  sulphide  in  water,  and 
test  the  solution  with  litmus  paper  (?).  What  ionic  substance 


§  77]  SULPHUR  69 

causes  this  reaction?  Which  of  the  two  substances  taken 
is  capable  of  furnishing  this  ion?  Formulate  the  interaction 
of  the  two  original  substances  and  explain  it  [R  375]. 

6.  Test  with  litmus  paper  the  solution  of  sodium  carbon- 
ate (?).  Explain  (Appendix  VI).  Of  what  sorts  of  radicals 
must  a  normal  salt  be  composed  in  order  that  the  solution  may 
show  an  alkaline  reaction  [R  344]  ? 

c.  Test  with  litmus  paper  the  solutions  of  cupric  sulphate  (?) 
and  ferric  chloride  (?),  and  account  for  the  result  [R  344].  Of 
what  sorts  of  radicals  must  a  normal  salt  be  composed  in 
order  that  the  solution  may  show  an  acid  reaction?  Why  is 
sodium  chloride  solution  neutral?  Define  hydrolysis. 

77.   Sulphur  Dioxide. 

a.  Touch  with  a  warm  platinum  wire  a  bit  of  sulphur,  and 
bring  the  wire  with  the  adhering  sulphur  again  into  the  flame. 
Withdraw,  and  note    the  color  of   the  flame  of   the    burning 
sulphur  and  also  the  odor  (?). 

b.  Heat  in  a  hard  glass  test-tube  a  few  particles  of  iron 
pyrites.     What  is  the  sublimate?    What  gas  is  evolved? 

c.  [Hood]     If  sulphur  dioxide  gas  is  not  furnished  in  the 
laboratory  from  cylinders  of  the  liquid,*  it  may  be  prepared  for 

use  in  78  or  83  as  follows:   Fit   up  a  

flask  (250  c.c.)  as  in   Fig.    8    (p.  20),         «         rN  S, 

and  attach  to  it  by  rubber  connections  M>HL 

a  gas  washing-bottle  (Fig.   18).     This  SSf 

bottle  is  to  serve   here    as    a    safety  J    TL 

vessel  (why  and  how?)  and  is  to  be 
left  empty.  If  78  is  to  be  performed, 
a  second,  similar  gas  washing-bottle 
will  be  required  to  dry  the  gas,  and  — 
will  contain  enough  concentrated  sul- 
phuric acid  to  immerse  the  longer  tube 
to  a  depth  of  half  an  inch.  Attach  ^ 

the  empty  bottle  with  the  shorter  tube 
next  to  the  generating  flask  (why  not  the  reverse?).  Place 
about  10  g.  of  copper  nails  in  the  flask.  Test  the  apparatus 
to  see  that  it  is  air-tight.  Add  10-15  c.c.  of  concentrated 
sulphuric  acid. 

Heat  the  flask  and  contents  by  means  of  a  sand  bath. 
Leave  the  cork  out  at  first  and  suspend  in  the  acid  a  thermom- 
eter. Note  the  temperatures  at  which  chemical  action  becomes 
perceptible  (?)  and  at  which  it  is  conspicuous  (?).  Why  cannot 

*  If  the  gas  is  not  so  furnished,  77  and  78  should  be  taken  up  after 
82. 


70  SULPHUK  [I  78 

dilute  sulphuric  acid  be  used?    Connect  the  apparatus  and 
continue  heating  to  obtain  the  gas  needed  in  78  and  83. 

d.  Allow  the  generating  flask  with  its  contents  to  remain 
over  night,  and  then  examine  and  describe  all  the  contents  (?). 

78.  Molecular  Weight  of  Sulphur  Dioxide   [Quant.  Hood]. 
Clean  and  dry  a  250  c.c.  flask  and  provide  it  with  a  tightly 
fitting  cork.     Weigh  the  flask  and  cork.     This  gives  the  weight 
of  the  flask  filled  with  air.     Now  fill  it  completely  with  sulphur 
dioxide,  by  downward  displacement  of  air,  cork,  and  weigh 
again.     To  insure  its  being  full,  repeat  this  operation  till  no 
increase  in  weight  occurs.     Finally,  allow  the  gas  to  escape, 
and  determine  its  volume  by  filling  the  flask  with  water  up 
to  the   cork  and   weighing  again.     Observe  the  temperature 
and  pressure  of  the  atmosphere. 

To  obtain  the  weight  of  the  empty  flask  and  its  cork,  subtract 
from  the  weight  of  the  vessel  filled  with  air  the  weight,  under 
the  observed  conditions,  of  a  volume  of  air  equal  to  its  content 
(1  liter  of  pure,  dry  air  weighs  1.293  g.  under  normal  condi- 
tions, or  the  G.M.V.  holds  28.955  g.  of  air). 

The  difference  between  this  corrected  weight  and  that  of 
the  flask  filled  with  sulphur  dioxide  is  the  weight  of  the  latter. 
Reduce  the  volume  of  the  gas  to  normal  conditions  and  calcu- 
late the  weight  of  the  G.M.V.  (22.4  1.)  and  of  1  1. 

Enumerate  carefully  all  the  sources  of  error  to  which  you 
should  expect  this  way  of  determining  the  density  of  a  gas  to 
be  liable.  In  doing  this,  consider  each  detail  of  the  operation 
very  critically. 

79.  Preparation  of  Sulphuric  Acid  (Two  students  working 
together).     Obtain  a  distilling-flask  (25  c.c.),  rubber  connections 
for  a  safety  bottle,  a  screw-clamp,  and  a  Chapman  pump  from 
the  storeroom.     Fit  up  with  your  one-liter  bottle  the  apparatus 
as  in  Fig.  19.     Charge  the  hard  glass  tube  with  about  10  g.  of 
granular  pyrite,*  and  place  a  small,  loose  plug  of-  asbestos  just 
beyond  the  pyrite  to  retain  any  unburnt  sulphur.     Put  into  the 
distilling-flask   about   10  c.c.  of   pure  concentrated  nitric  acid 
[Side-shelf].     The  safety  bottle,  half  filled  with  water  to  show 
the  rate  at  which  air  is  being  drawn  through  the  apparatus,  is 
attached  to  the  water  pump.     The  total  air  admitted  is  regu- 
lated by    the  screw-clamp  between  the  pump  and   the  safety 
bottle)  while  the  proportions  which  pass  over  the  pyrite  and 

*  In  case  very  pure  pyrite  is  not  available,  it  is  better  to  depart 
from  the  common  manufacturing  process  by  substituting  a  boat  con- 
taining a  little  sulphur. 


§79] 


SULPHUR 


71 


which  carry  over  the  nitric  acid  vapor,  respectively,  are  regulated 
by  pinching  one  of  the  tubes  with  the  finger  and  thumb. 

First  heat  the  pyrite  in  a  very  slow  stream  of  air  until  the 
sulphur  burns.  Then  warm  the  nitric  acid,  and,  by  pinching 
the  tube  admitting  air  to  the  pyrite-burner,  divert  part  of  the 
air  current  so  that  it  may  carry  over  a  little  of  the  vapor  of 
the  acid.  Heat  the  pyrite  strongly  and  continuously.  Repeat 
the  introduction  of  air  laden  with  nitric  acid  at  intervals,  when- 


Fig.  19 

ever  the  disappearance  of  the  red  fumes  in  the  bottle  shows 
that  a  further  supply  is  needed. 

After  a  crust  of  white  crystals  (?)  has  formed  in  the  bottle 
(there  may  be  considerable  delay  before  crystallization  starts), 
remove  the  attachments  and  blow  the  gases  from  the  interior 
by  means  of  the  air  blast.  If  crystallization  fails  to  begin  after 
a  reasonable  time  (note  that  an  interaction  even  between  the 
molecules  of  gases  may  be  slow,  in  spite  of  the  completeness  of 
the  mixing),  the  cause  is  either  the  introduction  of  too  much 
water  along  with  the  nitric  acid,  or  the  high  temperature  pro- 
duced by  the  chemical  actions  taking  place  in  the  bottle.  Re- 
moving the  attachments  and  cooling  the  bottle  in  a  stream  of 
water  frequently  brings  crystallization  about. 

Add  4-5  c.c.  of  water  and  wash  down  the  crystals  with  it. 
Describe  all  that' happens.  If  more  of  the  product  is  required, 
the  apparatus  may  be  connected  up  again  and  a  further  supply 
of  sulphur  dioxide  drawn  into  the  bottle,  and  subsequently 


72  SULPHITE  [§  80 

more  nitric  acid  vapor  can  be  added.     Finally  any  remaining 
crystals  may  be  decomposed  by  water. 

Filter  the  liquid  in  the  bottle  through  a  very  small  filter 
paper  into  a  dish,  rinsing  the  bottle  with  2-3  c.c.  of  water,  and 
evaporate  on  the  sand  bath  [Hood]  until  the  liquid  begins  to 
fume  strongly  (?).  This  will  remove  any  nitric  or  nitrous  acid 
that  it  may  contain.  Use  the  result  for  80  a  and  6. 

80.  Properties  of  Sulphuric  Acid. 

a.  Dip  a  match-stick  into  the   liquid  from   79,   and   make 
marks  on  a  sheet  of  paper.     Set  both  paper  and   stick   on  a 
radiator  (?).     What  property  of  the  acid  is  here  observed? 

b.  After  the  acid  prepared  in  79  is  cold,  dilute  it  with  2-3 
volumes  of  water.     Test  the  solution  with  litmus  paper   (?). 
Add  to  it  barium  chloride  solution  (?).     To  learn  whether  the 
action  is  easily  reversible,  add  pure  hydrochloric  acid  to  the 
mixture  (?).     The  formation  of  this  precipitate,  and  its  insolu- 
bility, furnish  a  distinctive  test  for  what  radical?     Which  sub- 
stances contain  this  radical?    What  property  of  sulphuric  acid 
is  shown  in  6? 

c.  Pass  a  current  of  hydrogen  sulphide  through  2-3  c.c.  of 
concentrated  sulphuric  acid.     Note  the  odor  (?)  and  precipi- 
tate (?).     What  property  of  sulphuric  acid  is  shown  in  c?    What 
other  evidence  of  this  property  have  we  previously  observed 
(see  16  d  and  52)? 

d.  Place  a  small  piece  of  sulphur  in  2-3  c.c.  of  concentrated 
sulphuric  acid,  and  heat  (?).     Note  the  odor  (?). 

e.  Heat  a  little  charcoal  with  sulphuric  acid  and  note  the 
odor  (?).     What  property  of  sulphuric  acid  is  shown  in  d  and 
e?    Why  would  not  dilute  sulphuric  acid  show  this  property? 

/.  [Hood]  Take  2-3  c.c.  of  concentrated  sulphuric  acid  in 
a  test-tube.  Suspend  a  thermometer  so  that  the  bulb  is  com- 
pletely immersed  in  the  acid.  Heat  the  contents  of  the  tube 
by  means  of  a  small  flame  and  note  the  temperature  at  which 
any  effect  (?)  is  observed,  and  that  at  which  it  is  conspicuous. 
Relate  this  temperature  to  that  observed  in  77  c.  [CAUTION! 
During  the  heating  remember  that,  if  the  tube  should  crack, 
the  hot  acid  may  splash  on  the  clothes  and  hands  and  produce 
severe  burns.  Exercise  proper  caution.  Be  careful  not  to 
wash  out  this  tube  until  the  acid  has  cooled.] 

81.  Sulphuric  Acid  as  a  Dibasic  Acid. 

a.  (Two  students  working  together).  Fill  a  burette  with  a 
solution  of  potassium  hydroxide  made  as  in  66.  Add  15  c.c. 
of  concentrated  sulphuric  acid  slowly  to  35  c.c.  of  water  in  a 
beaker,  and  fill  another  burette  with  the  diluted  acid,  when  cold. 
Ascertain  as  in  66  what  volume  of  the  alkali  will  neutralize  5  c.c. 


§  83]  SULPHUR  73 

of  the  acid.  Concentrate  the  mixture  by  evaporating  to  about 
10  c.c.,  remove  the  dish  from  the  water  bath,  and  allow  the 
resulting  solution  to  crystallize.  Dry  the  crystals  on  filter 
paper.  To  a  second  portion  of  the  acid  (use  no  phenolphtha- 
lem.  Why?),  twice  as  great  as  before,  add  exactly  the  same 
amount  of  the  alkali.  Evaporate  to  about  5  c.c.  and  treat  as 
before. 

Compare  the  two  lots  of  crystals  as  regards  (a)  form,  (b) 
taste,  (c)  reaction  of  their  solution  towards  litmus.  Con- 
firm by  studying  the  same  properties  of  the  purer  substances 
found  on  the  side-shelf.  Explain  the  differences  between  your 
own  preparations  and  those  on  the  side-shelf,  if  any  are  observed. 
Explain,  in  terms  of  the  hypothesis  of  ions,  the  difference  in 
the  reactions  of  the  two  products  towards  litmus. 

Formulate,  study,  and  explain  the  actions,  as  in  64  a  (second 
par.).  Take  the  components  of  the  original  solutions  [R  346] 
one  by  one,  and  describe  what  happens  to  each,  (a)  during 
complete  neutralization,  (b)  during  semi-neutralization  in  the 
second  part  of  the  experiment. 

What  would  be  the  effect  of  heating  perfectly  dry  specimens 
of  each  of  the  salts  [R  390]? 

How  many  grams  of  potassium-hydrogen  sulphate  are  re- 
quired to  give  1  liter  of  a  solution  of  normal  concentration 
in  respect  to  (a)  potassium-ion,  (b)  hydrogen-ion,  (c)  sul- 
phate-ion? 

6.  Make  a  solution  of  sodium  bicarbonate  and  test  it  with 
litmus  paper  (?)  and  with  Congo  red  paper  (?).  Why  do  some 
acid  salts  show  little  or  no  acid  reaction  towards  indicators? 

Define  carefully,  and  illustrate,  the  terms:  normal  (neutral) 
salt,  acid  salt,  and  basic  salt  [R  359]. 

82.  Sulphates.     Place  some  ferric  sulphate  in  a  porcelain 
crucible    supported   on   the   clay  triangle,   and   heat   strongly 
[Hood]  with  the  blast-lamp,  continuing  the  heating  after  all 
the  water  has  been  driven  off(?).    What  are  the  properties  of  the 
vapor  given  off  (?),  and  what  is  it?    What  is  the  residue?    Re- 
late this  result  to  that  in  80  /.     Recall  action  of  heat  on  dehy- 
drated gypsum   (23  /).     Classify  the  sulphates  in  accordance 
with  this  distinction. 

83.  Properties  of  Sulphurous  Acid  [Hood].     Use  a  stream  of 
sulphur  dioxide  from  a  cylinder  of  the  liquefied  gas,  or  from  the 
apparatus  described  in  77  c. 

a.  Pass  a  stream  of  sulphur  dioxide  for  a  few  minutes  into 
a  test-tube  full  of  water.  Test  the  solution  with  litmus  paper  (?). " 
What  compound  is  present  in  the  aqueous  solution  of  the  gas? 
Note  also  the  odor  of  the  liquid  (?).  Formulate  the  interac- 


74  SULPHUR  [§  84 

tion,  showing  all  the  substances  present.    Divide  the  solution 
into  four  portions. 

b.  Boil  one  portion  persistently  [Hood],  noting  from  time  to 
time  the  odor  and  reaction  towards  litmus  (?).     In  respect  to 
the  result,  does  the  solution  of  this  gas  resemble  that  of  hydro- 
gen sulphide,  or  that  of  hydrogen  chloride? 

c.  To  another  portion  add  barium  chloride  solution  (?).     To 
ascertain  whether  this  action  is  easily  reversible,  add  excess  of 
pure  hydrochloric  acid  (?). 

d.  To  the  third  portion  add  bromine-water   (?)   until  the 
color  is  permanent  (?).     Now  add  barium  chloride  to  the  mix- 
ture (?)  and  then  pure  hydrochloric  acid  (?). 

What  chemical  properties  of  sulphurous  acid  are  illustrated 
in  a,  6,  c,  and  d,  respectively  ? 

e.  Leave  the  fourth  portion  of  the  sulphurous  acid  for  several 
days  exposed  to  the  air  in  an  open  test-tube  or  bottle.     Then 
add  barium  chloride  and  pure  hydrochloric  acid,  and  compare 
the  result  with  that  in  c. 

/.  To  2-3  c.c.  of  potassium  dichromate  solution,  add  three 
or  four  equivalents  (a  large  excess)  of  dilute  sulphuric  acid. 
What  substances  does  the  mixture  contain?  Lead  a  stream 
of  sulphur  dioxide  through  the  solution  until  no  further  change 
is  observed  (?). 

g.  Take  2-3  c.c.  of  potassium  permanganate  solution,  treat 
as  in  /  (?),  and  answer  the  same  questions  (?). 

h.  Fill  a  bottle  with  the  gas  by  downward  displacement, 
introduce  some  moistened  litmus  paper  or  grass,  and  close 
with  a  glass  plate  (?). 

What  properties  of  sulphurous  acid  are  illustrated  in  e,  /,  g, 
and  h,  respectively  ? 

84.   Sulphites. 

a.  To  1  g.  of  sodium  sulphite  add  any  dilute  mineral  acid 
(that  is  to  say,  one  of  the  common  acids,  but  not  an  organic 
acid  such  as  acetic)  (?).  Formulate  this  action  completely. 

6.  Dissolve  a  minute  amount  of  sodium  sulphite  in  water 
and  add  bromine-water  in  excess  (test?  The  color  must 
remain).  Remove  the  excess  of  bromine  by  boiling.  Add 
barium  chloride  solution  (?)  and  then  pure  hydrochloric  acid  (?). 
Compare  this  experiment  with  that  in  83  d,  consider  whether  it 
is  probably  the  molecular  sodium  sulphite,  or  the  sulphite-ion, 
which  is  oxidized,  and  make  the  equation  accordingly. 

c.  Heat  persistently  about  1  g.  of  sodium  sulphite  in  a  porce- 
lain crucible,  supported  on  the  clay  triangle  over  a  blast-lamp. 
When  cool,  acidify  with  hydrochloric  acid  (?)  and  note  the 
odor.  If  any  sulphur  is  precipitated,  account  for  its  formation. 


§  86]  SULPHUR  75 

d.  Place  about  1  g.  of  sodium  bisulphite  in  a  hard  glass 
test-tube  and  heat  cautiously  with  the  tube  in  a  horizontal 
position  (why?).  Note  the  odor  (?)  and  whether  any  vapor 
condenses  (?).  This  behavior  is  typical  of  that  of  many  acid 
salts.  Why  is  the  behavior  of  potassium  bisulphate  somewhat 
different  (81  a)?  What  would  be  the  final  effect  of  heating 
sodium  bisulphite  more  strongly  and  for  a  longer  time? 

85.  Thiosulphates. 

a.  Dissolve  about  5  g.  of  sodium  sulphite  in  about  20  c.c.  of 
water  in  a  small  flask.     Add  4-5  g.  of  flowers  of  sulphur  to  the 
solution  and  boil  gently  over  a  small  flame  for  10-15  minutes. 
Filter  off  the  clear  yellow  solution  and  divide  into  two  parts. 

b.  To  one  portion  add  excess  of  any  dilute  mineral  acid  (?). 
Note  the  odor. 

c.  Take  10  c.c.  of  potassium  iodide  solution  and  dissolve  in 
it  a  few  small  crystals  of  iodine  [R  235]  (?).     Now  pour  the 
second  portion  of  the  solution  from  a  slowly  into  this  mix- 
ture [R  396]  (?).     How  can  this  action  be  used  for  estimating 
the  quantity  of  free  iodine,  and  what  substance  then  acts  as 
the   indicator?    For  what  purpose  was   the  potassium  iodide 
employed? 

d.  Heat  persistently  about  1  g.  of  sodium  thiosulphate  in  a 
porcelain  crucible  over  a  blast-lamp  (?).     Note  the  appearance 
of  the  residue.     When  cold,  add  dilute  hydrochloric  acid  (?) 
and  identify  the  products.     If  any  odor  was  observed  during 
the  heating,  can  you  now  account  for  it? 

86.  Reduction  of  Sulphur  Compounds.    Mix  a  pinch  of  any 
salt  of  a  sulphur  acid  with  an  equal  amount  of  anhydrous 
sodium  carbonate.     Slightly  char  the  end  of  a  match  from 
which  the  head  has  been  removed,  and  rub  the  charred  part, 
which  should  be  about  an  inch  in  length,  with  a  heated  crystal 
of  hydrated  sodium  carbonate.    Moisten  the  above  mixture 
with  water,  place  some  of  it  on  the  end  of  the  match,  and  heat 
in  the  reducing  region  of  a  small  Bunsen  flame.     Put  the  result 
on  a  clean  silver  coin  lying  in  a  watch-glass  and  moisten  with 
one  drop  of  water  (?).    Then  add  some  dilute  mineral  acid  and 
note  the  odor  (?).    This,  known  as  the  "hepar"  test,  is  a  test 
for  sulphur  in  any  form  of  combination. 


CHAPTER  XII. 

THE    ATMOSPHERE,    NITROGEN,    AMMONIA. 

87.  Preparation  of  Nitrogen  from  Air.     Place  a  large  plug  of 
copper  turnings  in  the  center  of  a  hard  glass  tube.     Fit  with 
corks  and  short  glass  tubes,  and  connect  with  the  short  tube 
of  the  aspirator  (Fig.  7,  p.  16).      Fill  completely  with  water 
the  bottle  and  long  tube  of  the  aspirator  and  close  the  latter 
with  a  screw  clamp  [Storeroom].     Arrange   a  vessel  to  catch 
the  water  discharged.     Now  heat  the  copper  red-hot  and  then 
partly  open  the  clamp  so  as  to  allow  the  water  to  be  syphoned 
off  in  a  slow  stream.     The  air  will  pass  over  the  heated  copper. 
What  change  does  the  copper  undergo,  and  what  collects  in  the 
bottle?    After  three-fourths  of  the  water  has  run  out,  close  the 
clamp,  disconnect  the  hard  glass  tube,  attach  a  delivery  tube 
in  its  place,  elevate  the  end  of  the  syphon,  and  replace  the 
nozzle  by  a  small  funnel  supported  by  a  clamp.     Pour  water 
into  the  funnel,  and  drive  the  gas  over  into  a  bottle  of  water 
inverted   in   the   pneumatic   trough.     Ascertain   whether   this 
gas  supports  combustion.     Describe  the  gas  as  regards  color 
and  smell.     What  other  gaseous  substances,  besides  nitrogen, 
does  this  gas  contain?  • 

Other  ways  of  removing  oxygen  from  the  air  are  described 
elsewhere  (14,  88,  and  94  d). 

88.  Proportion  (by  Volume)  of  Oxygen  in  the  Air  [Quant.] 
(from    Cooley's   Laboratory   Studies).      Provide   a   large   test- 
tube  with  a  two-hole  rubber  stopper.     Into  one  hole  fit  a  short 
piece  of  glass  tubing  terminating  in  a  rounded  nozzle,  the  tip 
of  which  projects  but  little  beyond  the  bottom  of  the  stopper. 
Into  the  other  hole  fit  a  short  glass  rod.     Test  the  apparatus 
for  air-tightness.    Connect  the  upper  end  of  the  glass  tube  with 
a  short-stemmed  funnel  by  means  of  a  piece  of  rubber  tubing 
(15  cm.  long)  as  in  Fig.  20,  and  support  the  funnel  in  a  clamp. 

Disconnect  the  test-tube,  temporarily,  and  remove  the  glass 
rod  from  the  stopper.  Prepare  an  alkaline  solution  of  potas- 
sium pyrogallate  by  mixing  3  c.c.  of  pyrogallic  acid  solution 
with  20  c.c.  of  a  solution  of  potassium  hydroxide  specially 
prepared  for  this  experiment  [Side-shelf],  and  pour  this  into 
the  funnel.  Now  open  the  clamp  and  permit  this  solution  to 
fill  the  rubber  and  glass  tubes  completely  down  to  the  opening 
of  the  nozzle.  Replace  the  test-tube,  fitting  the  stopper  tightly 

76 


§  88]    ATMOSPHERE,  NITROGEN,  AMMONIA        11 

into  its  mouth.  Finally,  reinsert  the  glass  rod,  and  so  inclose 
a  volume  of  air  equal  to  the  content  of  the  test-tube  and  at  the 
temperature  and  pressure  of  the  atmosphere.  These  opera- 
tions should  consume  as  little  time  as  possible,  as  the  alkaline 
solution  gradually  absorbs  oxygen  from  the  air  of  the  room, 
and  thereby  becomes  useless  for  further  absorption. 

Now  open  the  clamp,  taking  care  not  to  warm  the  test-tube 
by  handling.     A  few  drops  of  the  alkaline  solution  will  enter 


Fig.  20 

the  test-tube,  and,  as  the  oxygen  is  absorbed,  more  of  the 
solution  will  flow  in.  Close  the  clamp  and  invert  the  test-tube 
once  or  twice  in  order  to  bring  the  liquid  thoroughly  in  con- 
tact with  the  inclosed  air.  Finally,  while  the  test-tube  is  in 
the  inverted  position,  reopen  the  clamp  and  equalize  the 
levels  of  the  liquid  in  test-tube  and  funnel  by  raising  or  lower- 
ing the  former.  Then  close  the  clamp,  restore  the  test-tube 
to  its  original  position,  and  mark  the  positions  of  the  surface 
of  the  liquid  and  of  the  bottom  of  the  stopper  by  means  of 
paper  labels  or  rings  cut  from  rubber  tubing. 


78        ATMOSPHEKE,  NITEOGEN,  AMMONIA    [§  89 

Disconnect  the  test-tube  and  wash  out  the  liquid,  taking  care 
not  to  get  the  alkaline  solution  upon  the  hands.  Then,  by 
means  of  a  burette  filled  with  water,  measure  the  volumes 
required  to  fill  the  test-tube  up  to  the  lower  and  upper  marks 
respectively.  The  former  is  the  volume  of  the  oxygen,  the 
latter  that  of  the  air.  Calculate  the  percentage  of  oxygen  in 
the  air  by  volume. 

89.  Other  Components  and  Density  of  Air. 

a.  Place  2-3  c.c.  of  clear  barium  hydroxide  solution  in  the 
bottom  of  a  small  beaker  and  leave  it  exposed  to  the  air  for 
some  hours  (?). 

b.  Blow  air  from  the  lungs  through  a  glass  tube  into  2-4  c.c. 
of  clear  barium  hydroxide  solution  (?).     Explain. 

c.  How  may  the  presence  of  aqueous  vapor  in  air  be  demon- 
strated (27  a)?     How  may  its  quantity  be  measured? 

d.  The  weight  of  a  measured  volume  of  air,  or  of  nitrogen, 
may  be  determined  by  the  method  described  in  112.     From 
the  data  so  obtained  the  density  may  be  calculated. 

90.  Nitrogen. 

a.  Place  about  10  g.  of  pure  sodium  nitrite  and  about  8  g. 
of  ammonium  chloride  in  a  250  c.c.  flask  fitted  with  safety  and 
delivery  tubes  (Fig.  8,  p.  20).     If  b  is  to  be  performed,  insert 
between  the  flask  and  the  delivery  tube  a  U-tube  containing 
calcium  chloride  for  drying  the  gas.  . 

Clamp  the  flask  by  the  neck  to  a  ring-stand,  add  about  15  c.c. 
of  water,  and  warm  gently  [CAUTION!].  As  soon  as  the  action 
begins  remove  the  flame,  bring  a  dish  of  cold  water  under  the 
flask,  and  cool  it  for  a  few  seconds  at  a  time  so  that  the  action 
may  not  become  too  violent,  but  may  run  uniformly.  After 
sufficient  time  has  been  allowed  for  the  displacement  of  air 
from  the  apparatus,  fill  a  bottle  with  the  gas  over  water  in  a 
pneumatic  trough.  Has  the  gas  odor  or  color?  Does  it  sup- 
port combustion? 

b.  (Two  students  working   together).     In  a  piece   of  hard 
glass  tubing,  fitted  with  corks  and  short  pieces  of  glass  tubing, 
place  a  porcelain  boat  half  filled  with  powdered  magnesium. 
Connect  one  end  of  this  tube  to  the  outlet  tube  of  the  flask  in 
a   generating  nitrogen.     Heat   the   magnesium   strongly    (two 
Bunsen  burners  may  be  necessary).     What  action  is  noticed? 
What  is  the  color  of  the  product?    Transfer  the  contents,  when 
cold,  to  a  dry  test-tube,  close  with  a  cork,  and  use  in  91  b. 
May  the  same  product  be  formed  when  magnesium  is  heated  in 
the  air?    What  other  compound  would  be  formed  under  the 
latter  conditions? 


§  92]    ATMOSPHERE,  NITKOGEN,  AMMONIA        79 

91.  Ammonia. 

a.  Fit  a  small  flask  with  a  cork  and  L-shaped  exit  tube,  and 
fonnect  the  latter  with  a  U-tube.     Put  a  little  water  in  the 
bend  of  the  latter  so  as  just  to  close  the  passage.     Test  the 
apparatus  for  air-tightness.     Place  in  the  flask  a  mixture  of 
powdered  quicklime  and  ammonium  chloride,  about  10  g.  of 
each,   and  warm  gently  [Hood].     After  the  air  has  been  dis- 
placed, the  whole  of  the  gas  should  dissolve  in  the  water.     Use 
this  solution  of  ammonium  hydroxide  in  92. 

If  required  to  determine  the  density  of  ammonia,  which  of 
the  various  methods,  should  you  select  (15  a,  78,  or  112)? 

b.  To  the  product  from  90  b  add  a  little  water,  boil,  and 
note  the  odor  (?).     What  other  substances  would  behave  in  the 
same  way  as  magnesium  nitride? 

e.  Heat  a  small  piece  of  gelatine  in  a  dry  test-tube  and  note 
the  odor  (?). 

92.  Ammonium  Hydroxide:    An  Inactive   Base:    Salts   of 
Amm  o  ilium . 

a.  Test  the  reaction  towards  litmus   paper  of   the  solution 
made  in  91  a  (?).     What  substance  is  present?    Hold  a  glass 
rod  dipped  in  concentrated  hydrochloric  acid  over  the  solu- 
tion (?).     What  substance  is  shown  by  this  test  to  be  present? 
Formulate  the  relations  (in  equilibrium)  of  all  the  substances 
in  the  solution. 

b.  Expose  1-2  c.c.  of  the  solution  from  91  a  in  an  evaporat- 
ing-dish  for  24  hours  and  then  note  the  odor  (?)  and  test  with 
litmus  (?).     Heat  [Hood]  another  small  portion  in  an  evapo- 
rating-dish  for  some  minutes,  and  note  the  odor  from  time  to 
time  (?).     Does  the  aqueous  solution  of  this  gas  behave  like 
that  of  hydrochloric  acid,  or  like  that  of  hydrogen  sulphide? 
What  other  gases  resemble  ammonia  in  this  respect? 

c.  Neutralize  (test  ?)  the  remainder  of  the  solution  from  91  a 
with  dilute  sulphuric  acid  and  evaporate  to  dryness  on  a  water 
bath  (?).      Formulate  this  action  after  the  model  in  64  a  (sec- 
ond par.),  and  explain  what  happens  during  neutralization  to 
each  of  the  substances  present  in  the  ammonium  hydroxide 
solution. 

Scrape  the  residue  into  the  middle  of  the  dish,  invert  over  it  a 
small  funnel,  the  stem  of  which  has  been  closed  with  a  paper 
plug,  and  heat  the  dish  strongly  and  persistently  (?).  To  learn 
whether  the  sublimate  is  identical  with  the  residue,  examine  it 
for  the  ammonium  radical  (92  d,  below),  and  the  sulphate  (80  6) 
radical. 

d.  Dilute  1-2  c.c.  of  ammonium  chloride  solution  and  add  to 
ft  1-2  c.c.  of  sodium  hydroxide  solution  (?).    Note  the  odor  (?). 


80        ATMOSPHERE,  NITROGEN,  AMMONIA    [§  92 

Formulate,  study,  and  explain  this  action  according  to  the 
directions  in  64  a  (second  par.).  Include  in  the  formulation  the 
liberation  of  the  ammonia.  What  is  an  inactive  base? 

The  evolution  of  ammonia  when  an  active  base  is  added  to  a 
solution  of  any  ammonium  salt  is  used  as  a  test  for  the  latter. 
Why  would  not  simply  heating  the  salt  by  itself  (as  in  92  c  and  e) 
serve  as  a  test?  What  salt  of  ammonium  that  we  have  used 
gives,  when  heated,  no  ammonia? 

e.  Place  some  ammonium  chloride  in  the  middle  of  an  open, 
hard  glass  tube.  Support  this  in  a  very  slightly  inclined  (5°) 
position  by  means  of  a  clamp  attached  close  to  one  end.  Put 
pieces  of  moistened  litmus  paper  (both  colors)  in  each  end,  and 
heat  the  salt  strongly  (?).  Watch  closely  the  effect  on  the 
papers  at  each  end  (?).  What  does  this  experiment  show  to  be 
the  action  of  heat  on  ammonium  chloride?  Which  gas  appeared 
first  at  the  ends  of  the  tube,  and  why  first  at  both  lower  and 
higher  ends?  What  should  be  the  relative  speeds,  by  calcula- 
tion, of  the  two  gases  [R  108]  ?  Why  does  the  second  gas  reach 
the  ends  so  very  much  later  than  one  might  expect?  Has  gravity 
any  influence  on  the  result? 


CHAPTER  XIII. 

OXIDES  AND  OXYGEN  ACIDS  OF  NITROGEN. 

93.  Preparation  of  Nitric  Acid  [Hood].     Pulverize  about  10  g. 
of  sodium  nitrate  and  place  it  in  a  dry  retort  or  distilling-flask 
[Storeroom].     Cover  the  salt  with  concentrated  sulphuric  acid 
and  wait  until  this  liquid  has  permeated  and  moistened  the 
entire  mass.     Support  the  vessel  by  a  clamp  upon  a  sand  bath 
and  allow  the  neck  of  the  retort  (or  side-tube  of  the  flask)  to  ex- 
tend to  the  bottom  of  a  small  flask  (the  receiver).     In  order  that 
the  vapor  of  the  nitric  acid  may  condense,  this  flask  is  immersed 
in  a  vessel  of  cold  water,  and  is  covered  with  filter  paper  which  is 
continually  moistened.     Heat  the  retort  gently  until  a  sufficient 
amount  of  nitric  acid  has  been  obtained,  and  preserve  the  prod- 
uct in  a  corked  test-tube  for  use  in  97  a  [CAUTION!   Serious 
wounds  may  be  caused  by  allowing  this  liquid  to  come  in  contact 
with  the  skin].     What  is  the  composition  of  "concentrated" 
nitric  acid  [R  440],  and  how  does  the  acid  here  made  differ  from 
the  "  concentrated  "  acid  ?    What  law  teaches  us  to  expect  that 
the  former  will  be  more  active  (and  dangerous  to  handle)  than 
the  latter? 

94.  Nitric  Oxide. 

a.  Into  a  small  flask,  fitted  as  in  Fig.  8  (p.  20)  and  contain- 
ing about  10  g.  of  copper  nails,  pour  10-15  c.c.  of  water 
and  then  an  equal  amount  of  concentrated  nitric  acid  [Desk]. 
Collect  the  gas  evolved  over  water  in  the  pneumatic  trough. 
Note  the  color  of  the  gases  first  formed,  and  observe  the  color 
of  the  pure  gas  finally  collected  over  the  water.  Fill  two 
bottles  (for  6,  c)  and  the  large  test-tube  (for  d)  with  the  gas. 

The  production  of  colored  gases,  when  copper  is  added,  is 
used  as  a  test  for  nitric  acid. 

6.  Into  one  bottle  introduce  a  burning  match  (?).  Note 
also  the  effect  of  opening  this  bottle  to  the  air  (?).  This  effect 
may  be  used  as  a  test  for  nitric  oxide,  or,  conversely,  for 
oxygen.  -How  should  you  apply  it  for  each  of  these  pur- 
poses? 

c.  Into  the  second  bottle  lower  a  deflagrating  spoon  with  a 
very   little   burning,    red    phosphorus    (?).     What    change    in 
volume  does  the  gas  undergo  in  this  action? 

d.  Transfer  without  loss  the  nitric  oxide  in  the  test-tube  to 
a  small  beaker  filled  with  water  and  inverted  in  the  pneumatic 

81 


82  ACIDS   OF  NITKOGEN  [§  95 

trough.  Fill  the  test-tube  with  oxygen  and  add  this  to  the 
nitric  oxide  (?),  thus  securing  equal  volumes  of  the  gases. 
Shake  the  beaker,  keeping  the  mouth  well  immersed,  until  no 
further  change  occurs.  Transfer  the  remaining  gas,  which 
must  be  either  nitric  oxide  or  oxygen,  back  to  the  test-tube. 
Note  its  volume,  and  determine  what  gas  it  is  (?).  What 
relative  volumes  are  (a)  used  for  the  interaction  and  (b) 
required  by  the  equation? 

How  might  the  proportion  of  oxygen  in  the  air  be  deter- 
mined by  application  of  this  interaction? 

e.  Prepare  10  c.c.  of  a  concentrated  solution  of  ferrous- 
ammonium  sulphate  [Note  37,  p.  68]  (or  ferrous  sulphate)  and 
divide  into  three  portions.  Into  one  pass  a  gentle  stream  of 
nitric  oxide  (?).  Boil  the  liquid  (?). 

/.  Add  to  the  second  portion  of  ferrous-ammonium  sulphate 
solution  an  equivalent  amount  of  dilute  sulphuric  acid,  heat 
to  boiling,  and  add  nitric  acid  [Desk]  drop  by  drop  (mix  after 
each  drop)  until  there  is  no  further  action  (?).  What  gas  is 
liberated? 

g.  Dissolve  a  single  crystal  of  sodium  nitrate  in  1-2  c.c.  of 
water,  and  add  a  part  of  this  solution  to  the  remainder  of  the 
ferrous-ammonium  sulphate  solution  from  e.  Pour  concen- 
trated sulphuric  acid  cautiously  and  steadily  down  the  side  of 
the  test-tube  until  it  forms  a  considerable  layer  at  the  bottom 
of  the  tube.  Note  the  brown  ring  between  the  layers,  and 
explain  by  reference  to  e  and  /.  This  constitutes  a  delicate 
test  for  nitric  acid  or  a  nitrate.  In  what  way  does  the  avoid- 
ance of  mixing  (and  consequent  ring-formation)  contribute  to 
the  delicateness  of  the  test? 

h.  Take  2-3  c.c.  of  concentrated  nitric  acid  in  a  test-tube, 
warm  it  slightly,  and  lead  through  it  a  stream  of  nitric 
oxide  (?).  By  waiting  until  the  air  has  been  wholly  displaced, 
make  certain  whether  the  colored  gas  is  formed  by  an  inter- 
action of  the  nitric  oxide  with  the  nitric  acid,  or  simply  by 
contact  with  the  air  in  the  test-tube  (?). 

95.  Nitrogen  Tetroxide.  Fit  a  hard  glass  test-tube  with  a 
cork  and  L-shaped  exit  tube,  and  see  that  it  is  air-tight.  Place 
8-10  g.  of  lead  nitrate  in  the  tube  and  clamp  it  in  a  horizontal 
position.  Prepare  a  strong  solution  of  sodium  hydroxide  by 
dissolving  2  g.  of  the  solid  in  7  c.c.  of  water  and  allow  the 
delivery  tube  to  reach  the  bottom  of  this  solution.  Now  heat 
the  lead  nitrate  (?)  persistently  until  gas  is  no  longer  given  off, 
or  until  the  liquid  is  no  longer  soapy  to  the  touch.  If  all  the 
gas  is  not  absorbed  in  the  alkali,  test  the  escaping  bubbles  for 
oxygen  (?).  Use  the  solution  in  100  d. 


§  97]  ACIDS   OF  NITROGEN  83 

What  is  the  residue?  What  other  nitrate  have  we  decom- 
posed in  the  same  way  (36)?  This  behavior  when  heated  is 
typical  of  the  nitrates  of  the  heavy  metals,  and  may  be  used 
for  identifying  them.  Which  nitrates,  when  heated,  would 
leave  the  metal,  instead  of  the  oxide  [R  362]  ?  Why  do  com- 
mercial specimens  of  mercuric  oxide  [R  657],  when  heated  in 
the  preparation  of  oxygen,  frequently  give  off  a  brown  gas? 

96.  Principles  Involved  in  Making  Nitric  Acid. 

a.  Addition  of  copper  (94  a)  to  a  liquid  containing  nitric 
acid  gives  red  vapors.     Is  this  a  test  for  any  substance  con- 
taining the  nitrate  radical,  or  only  for  nitric  acid?    Dissolve  a 
little  sodium  nitrate  in  water,  add  a  copper  nail,  and  warm  (?). 

b.  Was  nitric  acid  formed  in  93  on  mixing  sodium  nitrate 
and  sulphuric  acid,  before  the  distillation  began?    Solve  this 
question  by  mixing  sodium  nitrate   (finely  pulverized)   with 
concentrated  sulphuric  acid,  adding  a  very  little  water  [CAUTION] 
and  agitating  for  a  minute  or  so.     Lower  a  glass  rod  dipped  in 
ammonium  hydroxide  solution  into  the  test-tube  (?).     Apply 
also  the  copper  test  as  in  a  (?). 

c.  Is  the  action  of  sulphuric  acid  upon  sodium  nitrate  rever- 
sible?   Take  2-3  c.c.  of. concentrated  sodium-hydrogen  sulphate 
solution  and  add  to  it  an  equal  or  even  greater  volume  of  pure 
[Side-shelf]  concentrated  nitric  acid.     Cool  the  mixture  in  a 
stream  of  cold  water  and  stir  with  a  glass  rod  (?).     The  salt 
solution  must  be  sufficiently  concentrated,  otherwise  the  ex- 
periment will  fail.     Examine  with  a  lens  the  crystalline  product 
that    separates    out    (?).     If   the    action   is   reversible,    what 
enabled  us  to  obtain  a  large  yield  of  nitric  acid  in  93? 

d.  Will  other  acids  behave  like  sulphuric  acid?    Mix  some 
pulverized  sodium  nitrate  with  phosphoric  acid,  agitate  for  a 
minute  or  two,  and  apply  the  copper  test  as  in  a  (?).     Could 
phosphoric  acid  be  used  in  the  preparation  of  nitric  acid  as  in 
93?    Why?    Could    hydrochloric  acid  be  used    [R   182,  440, 
448]?    Could  hydrofluoric  acid  be  used  [R  241,  440]?    Give 
reasons  for  your  answers. 

97.  Properties  of  Nitric  Acid. 

a.  If  93  was  performed,  note  the  color  of  the  sample  (?). 
Blow  some  air  from  the  blast  through  the  acid  (?).  What  is 
the  color  of  pure  nitric  acid?  To  what  substance  was  the  color 
of  this  sample  due,  and  by  what  action  was  it  formed?  What 
property  of  nitric  acid  does  its  formation  indicate?  Blow  the 
moist  air  of  the  breath  over  this  specimen  (?).  What  property 
does  this  indicate?  Determine  the  boiling-point  of  anhydrous 
nitric  acid  by  boiling  this  sample  in  a  distilling-flask  with  a 
thermometer  immersed  in  the  vapor  (?). 


84  ACIDS   OF   NITROGEN  [§  97 

6.  Test  dilute  nitric  acid  with  litmus  paper  (?). 

c.  Add  1  g.  of  sulphur  to  2-3  c.c.  of  concentrated  nitric  acid 
and  boil  [Hood]  for  two  or  three  minutes  (?).     Is  there  any 
evidence  of  action?     Pour  the  clear  liquid  into  another  test- 
tube,  dilute  with  water,  and  test  for  the  sulphate  radical  (?). 
What  property  of  nitric  acid  is  here  shown? 

d.  The   interaction   of   dilute    (16   c)    and   of   concentrated 
(16  d)  sulphuric  acid  with  metals  has  already  been  studied. 
Try  the  action  of   (a)    magnesium  and    (b)    zinc,   separately, 
either  upon  dilute   or  upon  concentrated  nitric   acid,  and   of 
(c)  copper  upon  both,  and  explore  the  whole  action  thoroughly 
in  each  of  the  four  cases  as  follows : 

Fit  up  a  side-neck  test-tube  with  a  dropping-funnel  passing 
through  a  perforated  cork,  and  attach  a  delivery  tube  (or  use 
an  ordinary  test-tube  with  cork  and  delivery  tube).  Place  a 
small  amount  of  the  metal  in  the  tube  and  admit  the  acid 
from  the  dropping-funnel.  After  the  air  has  been  displaced, 
collect  the  gas  over  water  in  a  test-tube  inverted  in  the  pneu- 
matic trough  (or  in  an  evaporating-dish). 

If  the  gases  in  the  generating  tube  remain  colored,  nitrogen 
tetroxide  is  present.  If  the  gas  is  at  first  colored,  but  becomes 
colorless,  nitric  oxide  is  present:  confirm  by  admitting  air  to 
the  tube  in  which  it  has  been  collected  (?).  Hydrogen,  if 
liberated  alone,  would  show  neither  of  these  properties,  but 
might  be  identified  by  its  inflammability  (?).  If  both  hydro- 
gen and  nitric  oxide  are  liberated,  why  may  we  not  feel  confi- 
dent of  being  able  to  cause  the  former  to  burn  when  thus 
diluted?  How  can  the  nitric  oxide  be  separated  (94  d  or  e) 
so  as  to  leave  the  hydrogen  in  an  inflammable  condition? 
Examine  the  gas  in  each  case  for  these  three  substances. 

If  ammonia  is  formed  in  any  of  these  four  cases  by  complete 
reduction  of  the  nitric  acid,  where  will  it  be  found,  and  in  what 
condition?  (Consider  all  the  circumstances  carefully,  or  you 
will  answer  wrongly.)  Test  for  its  presence  (92  d)  (?).  Evap- 
orate on  a  water  bath  [Hood]  the  solution  remaining  in  the  test- 
tube  after  any  one  of  these  experiments  (?).  Collect  the  residue 
and  heat  it  in  a  dry  test-tube  (?).  In  what  form  of  combination 
was  the  metal  (95)? 

e.  Grasp  a  test-tube  by  means  of  a  strip  of  folded  paper  (Fig.  5, 
p.  14),  place  in  it  a  piece  of  granulated  tin,  and  add  some  con- 
centrated nitric  acid(?).     When  the  action  has  exhausted  itself, 
add  much  water  and  boil.     Fit  a  small  filter  paper  carefully  into 
a  funnel  [Note  24,  p.  9],  collect  the  solid  product  upon  the  filter 
and  wash  [Note  38,  below]  precipitate  and  paper  with  water. 
Test  the  filtrate  as  it  runs  through  to  see  whether  it  becomes 


§  99]  ACIDS   OF  NITKOGEN  85 

neutral  (?).  Spread  the  filter  paper  with  the  precipitate  upon  a 
water  bath  or  radiator  to  dry  and  ascertain  as  in  95  whether  the 
product  is  a  nitrate  (?).  Why  would  the  test  in  94  g  be  unsuit- 
able here? 

/.  Comparing  dilute  and  concentrated  nitric  acid  with  the 
same  forms  of  sulphuric  acid,  what  points  of  resemblance  and  of 
difference  have  you  observed? 

Account  for  the  differences  in  the  actions  of  dilute  and  of  con- 
centrated nitric  acid  in  c,  d,  and  e,  in  respect  to  the  gaseous  prod- 
uct of  reduction  which  is  typical  of  each. 

g.  Dip  a  piece  of  wool  in  concentrated  nitric  acid,  or  note 
the  nature  of  the  products  formed  when  the  acid  falls  upon 
the  hands  or  clothing  (?).  Would  cotton  behave  in  the  same 
way?  Explain  [R  441]. 

h.  To  1-2  c.c.  of  nitric  acid  add  3-4  c.c.  of  pure,  concen- 
trated hydrochloric  acid,  warm  gently,  and  note  the  appear- 
ance and  odor  (?).  Will  these  acids,  singly,  attack  all  metals? 
Explain  (?).  What  metals  are  attacked  only  by  the  mixture 
(aqua  regia),  and  why?  What  form  of  combination  do  the 
metals  assume? 

Note  38. — In  filtering,  observe  the  directions  in  Note  24.  To 
wash  a  precipitate  first  let  the  mother  liquor  drain  away  completely 
and  press  the  precipitate  with  a  spatula.  Then  cover  the  contents 
of  the  funnel,  including  the  whole  paper  (why?),  completely  (and 
repeatedly,  if  necessary)  with  the  washing  material.  When  the 
washing  is  complete,  dry  the  product  by  pressing  with  dry  filter 
paper. 

98.  Nitrous  Oxide. 

a.  In  a  test-tube  or  small  flask  provided  with  a  cork  and 
delivery  tube  (Fig.  10,  p.  24),  place  10  g.  of  ammonium  nitrate. 
Heat  cautiously  with  a  small  flame  [CARE!],  and,  after  the  air 
has  been  expelled,  collect  the  gas  in  two  bottles  over  water 
(warm  water,  if  available.       Why?).     Why  is  the  stream  of 
gas  so  slow,  relatively  to  the  vigor  of  the  action?    What  are 
the  relative  volumes  of  the  products  at  100°  ? 

b.  Into  one  bottle  lower  a  glowing  splinter  of  wood  (?). 

c.  Into  the  other  bottle  lower  a  deflagrating  spoon  contain- 
ing a  very  little  burning,  red  phosphorus  (?).     If  this  experi- 
ment were  to  be  conducted  in  a  closed  vessel,  what,  if  any, 
change  in  pressure  would  be  observed  after  the  products  had 
cooled? 

99.  Nitrates. 

a.  How  does  lead  nitrate  behave  when  heated?  What  other 
nitrates  behave  like  it?  How  does  ammonium  nitrate  behave 
when  heated? 


86  ACIDS   OF  NITROGEN  [§  100 

b.  Take  2-3  g.  of  sodium  nitrate  in  a  hard  glass  test-tube, 
and  heat  strongly  and  persistently  until  the  evolution  of  gas 
ceases.  Test  the  escaping  gas  for  oxygen.  Use  the  residue  in 
100  a.  What  nitrates  behave  in  this  way  when  heated? 

100.  Nitrites  and  Nitrous  Acid. 

a.  When  the  residue  from  99  b  has  cooled,  add  not  more  than 
3  c.c.  of  water,  shake  vigorously  until  the  whole  has  dissolved, 
and  divide  into  three  parts.     To  one  portion  add  dilute  sul- 
phuric acid  (?).     How  could  a  nitrite  be  distinguished  from  a 
nitrate? 

b.  To  5  c.c.  of  starch  emulsion  add  a  drop  of  potassium  iodide 
solution  and  some  dilute  sulphuric  acid,  and  then  introduce  a 
little  of  the  solution  from  a  (?). 

c.  Dilute  1-2  c.c.  potassium  permanganate  solution  with  a 
large  excess  of  dilute  sulphuric  acid,  and  add  a  drop  of  this 
mixture  to  the  solution  from  a  (?).     The  actions  in  a,  6,  and  c 
serve  for  the  detection  of  nitrites  and  nitrous  acid.     What  other 
characteristic  property  of  nitrites  has  been  encountered  (90  a)  ? 

d.  Examine  now  the  solution  obtained  by  leading  nitrogen 
tetroxide  into  sodium  hydroxide  (96).     Take  a  portion  of  the 
solution  and  acidify  (test?)  with  dilute  sulphuric  acid  (?).     To 
the  mixture  add  a  drop  of  diluted  potassium  permanganate 
solution  (?)  or  some  starch  emulsion  containing  a  drop  of  potas- 
sium iodide  (?).     What  substance  was  present? 

To  ascertain  whether  this  alkaline  solution  contains  a  nitrate 
as  well  as  a  nitrite,  the  latter  must  first  be  eliminated.  To  the 
remainder  of  the  alkaline  solution,  transferred  to  a  small  flask, 
add  at  least  5  g.  of  ammonium  chloride  [Hood]  and  heat  to 
boiling  (?).  Explain  the  evolution  of  ammonia.  What  other 
gas  is  given  off  (90  a)  ?  When  the  action  is  entirely  over,  add 
about  10  c.c.  of  water,  and  shake.  Prepare  2-3  c.c.  of  a  concen- 
trated solution  of  ferrous-ammonium  sulphate  [Note  37,  p.  68] 
(or  of  ferrous  sulphate),  add  to  it  1-2  c.c.  of  the  solution  to  be 
examined,  and  complete  the  test  for  a  nitrate  described  in 
94  g  (?).  Write  now  the  equation  for  the  action  of  nitrogen 
tetroxide  on  sodium  hydroxide. 

101.  Active    (Nascent)    State    of   Hydrogen.     Dilute    some 
potassium  permanganate  solution  with  water,  and  add  an  equal 
volume  of  dilute  sulphuric  acid  to  it.     Divide  into  two  parts. 
Through  one  pass  a  stream  of  hydrogen  gas  from  the  laboratory 
supply  or  from  a  Kipp's  apparatus  (?).     To  the  second  add  some 
zinc  dust,  and  shake  (?).     Interpret  the  result. 


CHAPTER  XIV. 

PHOSPHORUS. 

102.  Phosphorus.     What    difference    in    general    chemical 
behavior  do  the  two  allotropic  modifications  of  phosphorus 
exhibit  [R  459]  ?    What  product  is  formed  when  phosphorus 
burns  in  excess  of  oxygen,  and  what  is  formed  when  the  oxygen 
is  limited  in  amount  [R  464]  ? 

103.  Phosphine  [Hood].     Place  a  very  small  piece  of  cal- 
cium phosphide  in  a  little  water  in  a  beaker  (?).     What  mode 
of  forming  ammonia  is  similar  to  this,  and  how  is  it  similar? 
Repeat,  using  dilute  hydrochloric  acid  instead  of  water   (?). 
What  mode  of  forming  hydrogen  sulphide  is  similar  to  this, 
and  how  is  it  similar?     In  what  ways  does  phosphine  differ 
from  ammonia  [R  461]  ?    Which  of  the  differences  are  shown 
in  these  experiments?    Why  should  we  expect  ammonia  and 
phosphine  to  be  alike?    Test  with  litmus  the  water  in  which 
the  calcium  phosphide  was  placed  (?),  and  explain. 

104.  Metaphosphoric  Acid. 

a.  Throw  2  g.  of  phosphorus  pentoxide,  in  minute  portions 
at  a  time,  into  a  beaker  containing  10  c.c.  of  cold  distilled 
water  (?).  Allow  the  liquid  to  stand  for  a  few  minutes,  or 
until  clear.  Test  the  liquid  with  litmus  paper  (?).  What 
acid  is  present  [R  464]  ?  Use  the  solution  for-  b  and  c  and  105  a. 
Why  could  not  the  product  made  by  burning  phosphorus  in  a 
closed  volume  of  air  be  used  in  this  case? 

6.  To  a  part  of  the  solution  from  a  add  silver  nitrate  solu- 
tion, a  little  at  a  time,  shaking  between  additions,  until  a  per- 
manent precipitate  (color?)  is  formed  (?).  Is  an  action  like 
this  reversible?  Is  this  action  incomplete?  To  answer,  add 
one  or  two  drops  of  diluted  (1  : 4  Aq.)  ammonium  hydroxide 
solution,  observe  whether  the  precipitate  increases,  and  ex- 
plain. This  is  a  reaction  of  what  ion?  What  other  substances 
would  give  it? 

c.  To  1  c.c.  of  albumen  solution,  add  one  or  two  drops  of 
the  solution  from  a  [R  468]  (?).  This  is  a  reaction  of  the  free 
acid  only,  and  not  of  metaphosphate-ion. 

105.  Orthophospnoric  Acid. 

a.  Dilute  the  remainder  of  the  solution  of  metaphosphoric 
acid  from  104  a  with  10  c.c.  of  water,  and  boil  in  a  small  flask 
vigorously  for  an  hour  or  more.  If  necessary  add  more  water 

87 


88  PHOSPHORUS  [§  106 

to  make  up  for  the  loss  by  evaporation.  Cool  the  solution, 
treat  portions  of  it  with  silver  nitrate  and  with  albumen,  as  in 
104  6  and  c,  and  answer  the  same  questions.  How  may  the 
formation  of  this  acid,  during  the  boiling,  be  hastened  [R  465]? 

6.  Heat  1  g.  of  red  phosphorus  with  5  c.c.  of  slightly  diluted 
nitric  acid  in  a  test-tube  (?).  When  the  action  has  ceased, 
filter,  if  necessary,  and  drive  off  the  water  and  excess  of  nitric 
acid  completely  by  evaporation  [Hood]  on  a  water  bath.  Mix 
with  a  few  drops  of  concentrated  nitric  acid  the  syrup  which 
remains,  and  evaporate  once  more.  It  is  essential  that  all  the 
nitric  acid  be  finally  removed  (why?).  Redissolve  the  syrup 
in  water  and  test  with  litmus  paper  (?). 

Treat  part  of  the  solution  with  silver  nitrate  as  in  104  b, 
and  answer  the  same  questions  (a  black  precipitate  with  silver 
nitrate  is  due  to  phosphorous  acid  [R  469]  formed  by  incom- 
plete oxidation). 

c.  Take  5  c.c.  of  the  solution  of  ammonium  molybdate  in 
nitric  acid  [Side-shelf],  add  to  it  two  drops  of  the  solution  of 
orthophosphoric  acid  prepared  in  b,  and  warm  gently  (?). 
This  is  a  very  delicate  test  for  phosphoric  acid,  or  orthophos^ 
phate-ion. 

106.   Phosphates. 

a.  Take  some  sodium  phosphate  (secondary  sodium  ortho- 
phosphate)  solution  and  test  it  with  litmus  paper  (?).     What 
ions  are  present?    Are  acid  salts  always  acid  towards  litmus 
(74  6)?     If  not,  explain  why  they  are  not.     Explain  also  the 
actual  reaction  of  this  solution. 

b.  To  a  small  part  of  the  sodium  phosphate  solution  add 
silver  nitrate  solution  until  the  precipitation  is  complete  (?). 
What  is  the  precipitate  (see  106  a  and  b)  ?    What  are  the  reac- 
tions towards  litmus  of  the  sodium  phosphate  (a) ,  and  silver 
nitrate    solutions    singly?      Test    the    mixture    with    litmus 
paper  (?).    What  ion  is  evidently  formed,  and  what  product 
is  therefore  present? 

c.  Prepare  a  little  " magnesia  mixture"  by  adding  to  1  c.c. 
of  magnesium  sulphate  solution  a  few  drops  of  ammonium 
hydroxide  and  then  excess  of  ammonium   chloride  solution. 
Add  to  the  rest  of  the  sodium  phosphate  solution  a  little  of 
this    mixture    (?).     In    making   the    equation,    disregard    the 
ammonium  chloride,  which  is  added  only  to  prevent  precipita- 
tion of  magnesium  hydroxide.    This  is  another  test  for  the 
presence  of  what  ions? 

d.  Strongly  heat  [Blast-lamp]  2  g.  of  dry  sodium  phosphate 
in  an  open  crucible  for  twenty  minutes,  or  until  no  further 
change  is  observed  (?).     Dissolve  the  cold  mass  in  water  (it 


§  107]  PHOSPHORUS  89 

dissolves  very  slowly),  and  test  a  portion  of  the  solution  with 
silver  nitrate  solution  (?).  This  is  a  reaction  of  what  ion? 
Take  the  remainder  of  the  solution,  liberate  the  acid  (?)  by 
adding  acetic  acid,  and  introduce  a  few  drops  of  the  liquid 
into  a  solution  of  albumen  (?). 

Make  a  table  showing  the  effects  of  the  three  phosphoric 
acids  upon  albumen  and  the  colors  of  their  silver  salts.  How 
could  you  identify  salts  of  the  three  acids? 

e.  Heat  strongly  [Blast-lamp]  2  g.  of  microcpsmic  salt  as 
in  d.  Note  the  odor  (?)  and  reaction  towards  moistened  litmus 
paper  (?)  of  the  vapors  given  off.  Dissolve  the  residue  in  cold 
water  and  use  the  tests  tabulated  in  d  to  learn  what  salt  has 
been  formed. 

/.  Make  a  bead  on  a  straight  platinum  wire  as  in  3  c,  using 
microcosmic  salt  instead  of  borax.  Of  what  must  the  bead 
consist?  Now  fuse  with  it  (3  d)  a  minute  particle  of  cupric 
oxide  (?).  What  difference  do  your  experiments  show  as  to 
the  relative  stabilities  of  NaP03,  NaNO3  (99  6),  and  KC10, 
(16  a)? 

107.   Halides  of  Phosphorus. 

a.  What  were  the  actions  of  water  on  the  tribromide  (44  6) 
and  tri-iodide  (48  6)  of  phosphorus? 

b.  Place  2-3  c.c.  of  phosphorus  trichloride  in  a  dry  test- 
tube  and  blow  the  breath  over  the  tube  (?).     Add  water  drop 
by  drop  (?)  until  about  5  c.c.  has  been  used,  then  boil  the  solu- 
tion (Fig.  5,  p.  14).     Test   the   vapor  with   litmus  paper  (?) 
and  with  a  rod  dipped  in  ammonium  hydroxide  (?).     Evapo- 
rate [Hood]  the  solution  to  a  syrup  on  the  water  bath  (?). 

c.  Transfer  part  of  the  syrup  from  b  to  a  small  test-tube  and 
heat  until  the  gas  evolved  may  be  ignited  at  the  mouth  of  the 
tube   (?).     Note  the  odor  of  this  gas  before  igniting  it   (?). 
Continue  heating  until  the  action  is  over.     Ascertain  according 
to    106    d   which    of   the    phosphoric    acids    constitutes    the 
residue  (?). 

d.  Dilute  1  c.c.  of  potassium  iodide  solution  with  water  and 
dissolve  in  the  liquid  a  crystal  of  iodine.     Add  to  this  solution 
a  little  of  the  syrup  from  b,  and  shake  (?). 

e.  Place  upon  a  watch-glass  5  or  6  small  granules  of  phos- 
phorus  pentachloride   and   blow   the   breath   over   them    (?). 
Throw  them  into  2-3  c.c.  of  water  in  a  test-tube  (?)  and  boil. 
Test  the  solution  with  litmus  (?).     To  a  small  part  of  the  cold 
solution  add  excess  (test?)  of  silver  nitrate  solution  (?).     Fil- 
ter.    What  remains  upon  the  paper  (?).    To  the  filtrate  add 
diluted  (1:  4  Aq.)  ammonium  hydroxide  drop  by  drop  (shake 
between  drops)  (?). 


CHAPTER  XV. 

CARBON. 

108.  Charcoal. 

a.  Place  a  small  piece  of  charcoal  in  a  test-tube  half  full  of 
water   (?).     Now  hold  it  under  the  water  with  the   reverse 
end  of  the  file,  and  boil  the  water  for  several  minutes   (?). 
When  the  whole  has  cooled,  test  once  more  the  tendency  of 
the  charcoal  to  float  (?).     Explain. 

b.  Boil  dilute  solutions  of  litmus  and  indigo,   separately, 
with  pulverized   animal   charcoal,  and   filter  each   liquid    (?). 
The  activity  of  the  charcoal  is  much  increased  by  previous 
heating  in  a  covered  crucible. 

c.  Fit  a  hard  glass  test-tube  with  a  cork  and  L-tube.     Mix 
Intimately  in  the  mortar  1  g.  of  pulverized  cuj)ric  oxide  with 
1  g.  of  pulverized  wood  charcoal  and  place  in  tne  tube.     Heat 
persistently  [Blast-lamp]  and  pass  the  gases  through  5  c.c.  of  lime- 
Water  (?).     Examine  the  residue  by  rubbing  vigorously  under 
water  in  the  mortar  and  washing  away  the  lighter  particles  (?). 
What  property  of  carbon  is  here  illustrated? 

109.  Carbon  Dioxide. 

a.  Place  a  few  small  pieces  of  magnesite  (magnesium  car- 
bonate) in  a  hard  glass  test-tube  fitted  with  a  cork  and  L-tube 
and  heat  strongly.  Pass  the  gas  through  5  c.c.  of  lime-water 
in  a  test-tube  (?).  What  is  the  residue  [R  643]  ? 

6.  Fit  up  a  generating-flask  (Fig.  8,  p.  20)  and  connect  with 
two  wash-bottles  (Fig.  18,  p.  69)  containing  water  and  con- 
centrated sulphuric  acid,  respectively  (what  is  the  use  of  each 
of  these?  The  latter  is  unnecessary  if  110  is  omitted).  Place 
in  the  flask  some  pieces  of  marble  and  pour  upon  them  diluted 
hydrochloric  acid.  Collect  the  gas  in  two  bottles  by  down- 
ward displacement. 

What  substances  could  be  substituted  for  marble  in  this 
experiment?  What  other  sources  of  carbon  dioxide  have  been 
encountered  (13  c,  108  c,  109  a;  see  also  111  a  and  c,  113  b, 
114  b,  118)? 

c.  To  one  add  a  little  water,   close  with  the  hand,   and 
shake  (?).     Is  the  gas  soluble  in  water,  or  not  ? 

Use  the  second  to  compare  its  weight  with  that  of  air. 
Employ  baryta-water  as  a  test. 

d.  Take  two  test-tubes  containing  distilled  water,  pass  a 

90 


§  112]  CARBON  91 

current  of  the  gas  into  one,  and  test  each  with  litmus  paper  (?) . 
Boil  the  solution,  and  test  again  with  litmus  (?).  Explain. 

e.  Lead  the  gas  into  a  little  sodium  hydroxide  solution  in  a 
test-tube  until  the  solution  is  saturated  (test?  Note  36,  p.  67) . 
Let  the  solution  stand  until  it  dries  spontaneously  (first  residue) . 
Heat  the  dry  residue  (?)  in  a  test-tube,  and  determine  what  two 
things  are  given  off. 

To  this  residue  after  heating  (second  residue)  add  dilute 
hydrochloric  acid  until  all  action  (?)  ceases.  Evaporate  the 
solution  on  the  water  bath,  and  examine  and  taste  this  final 
residue  (?).  Having  recognized  the  products  of  the  last  action, 
and  taking  into  account  the  preceding  observations,  state  what 
the  nature  of  the  second  and  first  residues  must  have  been. 
Write  equations  for  all  actions. 

110.  Molecular  Weight  of  Carbon  Dioxide  [Quant.]. 

a.  Determine  the  weight  of  a  measured  volume  of  the  gas  by 
the  method  used  for  sulphur  dioxide  (78),  and  calculate  the 
weight  of  the  gram-molecular  volume.     What  further  informa- 
tion must  we  have  to  enable  us  to  determine  the  formula? 

b.  Use  the  quantitative  results  obtained  in  the  synthesis  of 
carbon  dioxide  (34)  along  with  this  molecular  weight,  to  calcu- 
late the  weights  of  carbon  and  of  oxygen  in  a  molecular  weight 
of  the  gas.     What  further  steps  are  necessary  in  order  to  fix 
the  atomic  weight  of  carbon? 

111.  Carbon  Monoxide. 

a.  Heat  about  10  g.  of  oxalic  acid  crystals  with  concen- 
trated sulphuric  acid  in  a  generating-flask  (Fig.  8,  p.  20),  and 
fill  a  bottle  over  water  with  the  gas  which  is  given  off.     Shake 
with  lime-water   (?).     With  what  substance  should  we  wash 
the  gas  to  remove  the  carbon  dioxide?    Arrange  a  wash-bottle 
to  purify  the  gas.     Fill  two  bottles  with  the  purified  gas  over 
water.    Test  one  with  lime-water  again   (?).     If  the  gas  is 
pure,  burn  that  in  the  other  bottle,  add  lime-water  at  once, 
close  quickly,  and  shake  (?). 

b.  Devise  a  way  of  ascertaining  roughly  the  relative  volumes 
of  the  two  gases  generated  in  a,  and  measure  the  proportion  in 
a  test-tube  full  of  the  mixed  gases. 

c.  Pass  a  stream  of  the  purified  carbon  monoxide  over  a 
little  pulverized  cupric  oxide,  heated  in  a  boat  in  a  hard  glass 
tube  (?).    What  gas  is  formed?    What  remains  in  the  boat? 
What  is  here  the  reducing  agent? 

112.  Molecular    Weight    of    Carbon    Monoxide    [Quant.]. 
Obtain  [Storeroom]  a  round-bottomed,  250  c.c.  flask.     Fit  it 
with  a  rubber  stopper  through  which  passes  a  short,  straight 
tube.    Attach  to  the  latter  a   short  piece  of  rubber  tubing 


92  CAKBON  [§  113 

closed  with  a  strong  pinch  clamp.  Make  a  mark  on  the  neck 
at  the  bottom  of  the  stopper,  so  as  to  be  able  to  measure  the 
exact  content  of  the  flask  up  to  the  stopper.  Place  30  c.c.  of 
water  in  the  flask,  insert  the  stopper,  remove  the  clamp,  and 
boil  the  water  with  a  small  flame  for  about  five  minutes,  so  as 
to  drive  out  all  the  air.  Close  the  rubber  tube  with  the  clamp 
and  remove  the  flame  quickly,  wipe  the  flask  and  allow  it  to 
cool.  When  it  has  assumed  the  temperature  of  the  air,  weigh 
the  whole  carefully,  suspending  the  flask  on  the  balance  by  a 
thread  tied  round  the  neck.  Connect  with  the  apparatus 
delivering  pure  carbon  monoxide,  and  open  the  clamp  a  very 
little  so  as  to  admit  a  slow  stream  of  the  gas.  When  the  flask 
is  full,  close  the  clamp,  disconnect  from  the  generating  appara- 
tus, open  the  clamp  for  an  instant  to  restore  the  pressure  to 
that  of  the  atmosphere,  and  weigh  again.  The  gain  in  weight 
represents  the  weight  of  the  carbon  monoxide.  Read  the 
barometer  and  thermometer.  Subtract  from  the  barometric 
reading  the  aqueous  tension  at  the  observed  temperature. 
Ascertain  the  volume  of  the  flask  by  filling  with  water  to  the 
mark  and  weighing  again. 

Calculate  the  weight  of  the  G.M.V.  of  the  gas. 

To  what  class  of  gases  would  this  method  of  determining  the 
density  and  molecular  weight  be  applicable?  Why  could  not 
this  method  be  used  for  carbon  dioxide? 

113.   Methane  (Marsh  Gas). 

a.  Pulverize  about  5  g.  of  fused  sodium  acetate  and  about 
20  g.  of  soda-lime    (a  mixture  of  quicklime  and  sodium   hy- 
droxide).    Mix  the  ingredients   intimately  in  the  mortar,  and 
place  in  a  large  test-tube  fitted  with  a  one-hole  cork  and  deliv- 
ery tube  (Fig.  6,  p.  15).    Rap  the  test-tube  gently  so  as  to  form 
a  space  for  the  passage  of  the  gas.     Then  clamp  the  tube  close 
to  the  cork  in  a  slightly  inclined  (5°)  position,  so  that  it  slopes 
toward  the  mouth  (why?).     Slip   over  the  tube   a  cylinder  of 
wire  gauze,  and,  beginning  at  the  rear  or  sealed  end,  heat  the 
contents  gently  until  the  evolution  of  gas  is  uniform.      When 
all  the  air  is  displaced,  collect  one  bottle  of  gas  over  water. 

Attach  a  small  nozzle  to  the  end  of  the  delivery  tube  and 
ignite  the  gas.  Note  the  color  and  degree  of  luminosity  of  the 
flame  (?).  Hold  over  the  jet  a  dry  inverted  beaker  and  observe 
one  product  of  the  combustion  (?). 

b.  Hold  the  bottle  containing    the  gas    mouth  downward 
and  apply  a  light  (?).     Quickly  pour  into  the  bottle  some  lime- 
water,  and  shake  (?).    What  volume  of  oxygen  is  required  for 
the  complete  combustion  of  one  volume  of  methane,  and  what 


§  115]  CAKBON  93 

ratio  will  the  resulting  volume  of  gases  bear  to  the  original 
volume  of  methane,  at  0°  and  at  100°,  respectively? 

114.  Ethylene  [Hood]. 

a.  Fit  a  250  c.c.  flask  with  a  doubly-bored  cork,  through 
which  pass  a  dropping-funnel  and  L-tube.  Attach  a  gas- 
washing  bottle  containing  a  little  water,  and  connect  an  L- 
shaped  delivery  tube.  Test  the  apparatus  to  see  that  it  is 
air-tight.  Place  in  the  flask  about  20  c.c.  of  phosphoric  acid, 
and  clamp  it  to  a  ring-stand  over  a  sand  bath.  Introduce  into 
the  bulb  of  the  dropping-funnel  (or  substitute,  36  b)  some 
alcohol.  Finally,  heat  the  phosphoric  acid,  and  when  it  has  had 
time  to  reach  220°,  admit  the  alcohol  drop  by  drop  beneath  the 
surface  of  the  phosphoric  acid  in  the  flask. 

6.  Fill  a  bottle  with  the  gas  over  water  and  apply  a  light  (?). 
Quickly  pour  some  lime-water  into  the  bottle,  and  shake  (?). 
Attach  a  nozzle  to  the  exit  tube  of  the*  washing-bottle  and 
raise  the  other  tube  clear  of  the  water  (why?),  ignite  the  gas, 
and  observe  the  luminosity  of  the  flame.  What  commercial 
use  has  ethylene  [R  513]  ?  Hold  a  cold,  dry  beaker  over  the 
flame  (?).  What  are  the  products  of  complete  combustion 
of  all  hydrocarbons? 

c.  Detach  the  nozzle,  reattach  the  delivery  tube  to  the  exit 
tube,  and  lower  the  other  tube  of  the  washing-bottle  once  more. 
Place  1  c.c.  of  bromine  [CAUTION!]  in  a  test-tube,  cover  it  with 
5  c.c.  of  water,  put  the  test-tube  into  a  beaker  filled  with  cold 
water,  and  allow  the  gas  to  bubble  into  the  bromine.  When 
the  color  of  the  bromine  has  disappeared,  examine  the  contents 
of  the  test-tube  (?).  Is  the  product  colored?  Is  it  soluble  in 
water?  What  do  you  infer  as  to  its  specific  gravity?  Detach 
the  dropping-funnel,  wash  it  out,  and  place  in  it  the  contents 
of  the  test-tube.  Draw  off  the  lower,  oily  layer  into  a  dry 
test-tube  and  note  its  odor  (?).  Try  its  solubility  in  alcohol  (?). 

Why  is  the  accepted  formula  for  ethylene  preferred  to  the 
simplest?  What  volume  of  oxygen  would  be  required  to  burn 
one  volume  of  the  gas  completely?  What  would  be  the  relative 
volumes  of  the  products  at  0°  and  100°,  respectively?  What 
volumes  of  bromine  vapor  and  ethylene  would  be  required  for 
complete  combination,  and  what  would  be  the  relative  volume 
of  the  product  (in  the  state  of  vapor)  ? 

115.  Acetylene.     Fill  a  test-tube  with  water  and  invert  it 
in  water  in  an  evaporating-dish.      Introduce  a  small  piece  ol 
calcium  carbide  under  the  mouth  of  the  tube  (?).     Test  the 
water  with  litmus  (?).     Bring  a  light  to  the  mouth  of  the 
tube  (?).     Note  the  luminosity  of  the  flame,  and  compare  with 
flames  of  methane  and  ethylene  (?). 


94  CARBON  [§  116 

Can  you  state  a  general  method  for  making  hydrides  of  non- 
metals  (such  as  C2H2,  PH3,  NHJ?  Can  SH2  [R  .645]  and  C1H 
[R  715,  718]  be  formed  similarly? 

116.  Illuminating -Gas. 

a.  Heat  some  sawdust  in  a  dry  test-tube   (?).    Note  the 
odor  (?),  reaction  towards  moist  litmus  paper  (?),  and  combus- 
tibility (?)  of  the  vapors.    What  is  the  residue? 

b.  Repeat  a,  using  bituminous  coal  (?). 

c.  Pulverize  a  few  particles  of  potassium  sulphate.    Take  a 
small  Bunsen  flame  and  reduce  the  supply  of  air  until  a  small 
luminous  region  appears.     Heat  the  platinum  wire,  touch  the 
salt  with  it,  and  hold  the  adhering  powder  steadily  in  the  lumi- 
nous part.     After  a  minute  or  two,  withdraw  the  bead,  place  it 
upon  a  clean  silver  coin  and  moisten  with  a  drop  of  water  (?) . 
Explain  the  result.    What  are  the  reducing  agents  used  here? 

117.  Acids. 

a.  To  1  g.  of  sodium  acetate  add  some  dilute  sulphuric  acid, 
and  warm.     Note  the  odor  (?).     How  could  you  use  this  action 
to  make  acetic  acid?    How  is  it  manufactured  [R  498]  ? 

b.  Take  5  c.c.  of  acetic  acid.    Test  with  litmus  paper  (?). 
Recall  its  interaction  with  zinc  or  iron  (16  e)  (?).    To  the  acid 
add  3-4  g.  of  litharge  and  boil  gently  for  a  few  minutes  (?).    Fil- 
ter, if  necessary,  while  hot,  and  set  the  clear  solution  aside  to 
crystallize  (?).     What  is  the  common  name  of  the  product  [R]? 

118.  Alcohol.     Dissolve  20  g.  of  glucose  syrup  in  150  c.c.  of 
water  and  add  yeast.     Fill  a  flask  to  the  base  of  the  neck  with 
the  mixture,  tie  a  piece  of  filter  paper  over  the  mouth  with 
thread  [Side-shelf],  and  set  the  whole  aside  in  a  warm  place  for 
3-4  days.     Then  warm  the  solution  and  test  the  gas  which  is 
given  off  for  oarbon  dioxide  (?). 

Filter  the  liquid  and  place  it  in  a  larger  flask,  fitted  with  a 
cork  and  L-tube,  and  connect  (Fig.  14,  p.  45)  with  a  con- 
denser [Storeroom].  Distil  off  about  50  c.c.  Place  the  distil- 
late in  a  distilling-flask  [Storeroom]  fitted  with  a  thermometer, 
boil  with  a  small  flame,  and  catch  the  part  which  passes  over 
between  75°  and  93°. 

Note  the  odor  of  the  distillate  (?).  Test  it  with  litmus 
paper  (?).  Use  one  drop  to  ascertain  whether  it  burns.  To 
the  rest  add  a  crystal  of  iodine  and  enough  sodium  hydroxide 
solution  to  dissolve  it.  Shake  vigorously,  and  do  not  add  more 
alkali  than  is  absolutely  necessary.  W^rm  the  solution  and 
then  cool  it  (?).  This  is  the  iodoform  test  for  alcohol. 

119.  Esters. 

a.  To  1  g.  of  sodium  acetate  add  1-2  c.c.  of  alcohol  and  1  c.c. 
of  concentrated  sulphuric  acid.  Warm,  if  necessary,  agitate 


§  119]  CARBON  95 

for  a  minute  or  two,  and  note  the  odor  (?).  This  is  a  test  for 
acetic  acid  or  an  acetate. 

b.  Place  in  a  porcelain  dish  a  piece  of  fat  the  size  of  a  pea, 
and  add  4  c.c.  of  alcohol  and  five  drops  of  a  50  per  cent  solu- 
tion of  sodium  hydroxide  (made  with  1  g.  of  the  solid  and  1  c.c. 
of  water).  Stir  constantly  and  boil  very  gently  until  the  odor 
of  alcohol  is  no  longer  perceptible,  then  stop.  The  alcohol  is 
used  as  a  common  solvent  for  the  fat  and  the  alkali.  What  is 
the  residue  [R  505]  ? 

Dissolve  the  soap  in  hot  water,  cool,  and  to  half  of  the  solu- 
tion add  dilute  hydrochloric  acid,  and  shake  vigorously  (?). 
Withdraw  the  floating  coagulum  by  means  of  a  glass  rod,  sus- 
pend it  in  water  in  a  test-tube,  add  a  few  drops  of  sodium 
hydroxide,  and  heat  until  solution  takes  place.  What  do  you 
conclude  from  its  solubility  in  the  alkali? 

To  the  other  half  of  the  soap  solution  add  calcium  chloride 
solution  (?).  Explain  the  action  of  hard  water  [R  594]  on  soap 
solution. 


CHAPTER  XVI. 

THE  ACTIVITY   OP  ACIDS  MEASURED  CHEMICALLY. 

120.  Estimation  of  the  Relative  Activity  of  Acids.  Charac- 
terize briefly  some  of  the  methods  available  for  measuring  the 
relative  activity  of  acids  [R  679]. 

a.  When  methyl  acetate  is  mixed  with  water,  it  undergoes 
hydrolysis  very  slowly,  acetic  acid  and  methyl  alcohol  being 
formed :  CH3.C2H302  +  H20  +±  CH3OH  +  HC2H302.  Add  about 
1  c.c.  of  methyl  acetate  to  10  c.c.  of  distilled  water  in  a  test- 
tube,  test  with  litmus  paper  (?),  and  cork  up  and  label  the 
mixture.  After  several  days,  test  once  more  with  litmus  (?). 

This  action  of  water  is  found  to  be  greatly  hastened  by  the 
addition  of  free  acids,  although  the  acids  remain  themselves 
unchanged  by  the  process.  Equivalent  quantities  (?)  of  dif- 
ferent acids  show  very  different  accelerating  powers  toward 
this  reaction.  The  order  in  which  they  are  placed  by  measure- 
ment of  this  particular  form  of  activity,  however,  is  the  same 
as  that  into  which  they  fall  when  compared  by  any  of  the  other 
methods.  The  extent  to  which  the  change  has  taken  place  can 
be  measured  at  any  moment  by  titration  with  alkali.  The 
quantity  of  acid  which  was  present  at  starting  being  known, 
the  quantity  found  is  the  same  acid  plus  the  acetic  acid  set 
free  by  the  progress  of  hydrolysis.  Subtraction  gives  the  quan- 
tity of  the  latter,  and  this  quantity  is  a  measure  of  the  activity 
of  the  accelerating  acid.  The  activities  of  hydrochloric  and 
sulphuric  acids  are  compared  in  ?>  by  this  method. 

6  (Two  students  working  together).  Procure  two  20  c.c. 
stoppered,  graduated  flasks,*  and  a  10  c.c.  and  a  1  c.c.  pipette 
[Storeroom],  Mark  the  flasks  with  a  file  so  as  to  be  able  to  dis- 


tinguish them,  and  into  one  measure  exactly  10  c.c.  of  normal 
(?)  hydrochloric  acid,  and  into  the  other  10  c.c.  of  normal  (?) 
sulphuric  acid.  Put  exactly  1  c.c.  of  methyl  acetate  into  each, 
and  fill  both  flasks  with  distilled  water  up  to  the  20  c.c.  mark 
at  once  (why  at  once?).  Stopper  the  flasks  tightly,  mix  the 
contents,  and  suspend  both  so  that  their  necks  are  just  above 
the  water  in  a  large  bath  (use  the  pneumatic  trough)  heated  to 

*  Instead  of  graduated  flasks,  common  flasks  with  cork  stoppers 
may  be  used.  Measure  into  each  flask  10  c.c.  of  acid  and  then,  with 
the  same  pipette,  10  c,c.  of  water.  Add  the  1  c.c.  of  methyl  acetate, 
shake,  and  proceed  as  directed. 

96 


§  120]  ACTIVITY   OF  ACIDS  97 

about  45°.  If  the  bath  is  fairly  large,  further  external  heating 
will  not  be  necessary.  Otherwise,  maintain  the  temperature  by 
means  of  a  small  flame.  In  accurate  work  the  temperature 
must  be  kept  constant  within  0.1°  during  the  experiment  by 
means  of  a  thermostat.  Allow  the  flasks  to  remain  in  this 
position  for  30  minutes  (<). 

While  this  is  going  on  make  some  normal  (or  approximately 
normal  =  4  per  cent)  sodium  hydroxide  and  fill  a  burette 
with  it.  Take  fresh  portions  of  10  c.c.  of  each  of  the  acids  and 
titrate  them  with  the  alkali,  using  two  drops  of  phenolphthalein 
as  an  indicator.  Record  the  results.  These  numbers  measure 
the  amount  of  mineral  acid,  at  starting,  in  each  flask. 

When  the  above  time  has  elapsed,  remove  both  flasks  from 
the  bath,  transfer  the  contents  of  each  to  a  separate  beaker, 
rinsing  out  the  flasks  with  distilled  water.  Add  two  drops  of 
phenolphthalein  to  each  portion  and  titrate  with  the  solution 
of  sodium  hydroxide  used  before.  The  difference  (d)  between 
the  volumes  of  alkali  required  for  the  neutralization  of  10  c.c. 
of  each  acid  with  and  without  methyl  acetate  represents  the 
amount  of  sodium  hydroxide  required  to  neutralize  the  acetic 
acid  liberated  in  the  hydrolysis.  The  two  values  of  d  obtained 
are  functions  of  the  activity  of  the  acids.  Which  acid  is  more 
active?  What,  according  to  the  theory  of  ionization,  is  really 
measured  in  these  experiments?  What  does  the  result  of  a 
show  water  to  be? 

Calculate  8,  the  speed  with  constant,  unit  concentration,  by 
the  formula  for  a  unimolecular  action  [R  252]  .  The  initial  con- 
centration (ct)  of  1:20  is  equal  to  0.67  moles  per  liter.^  The 
proportion  transformed  (cc),  which  must  be  expressed  in  the 
same  units,  is  d/20  moles  per  liter.  Then  8  =  1/t  loge, 
/c1/(c1—  £)}.  The  ratio  of  the  values  of  S  for  the  two  acids 
defines  their  relative  activities.  The  time  (£),  being  the  same 
for  both,  may  be  neglected,  and  common  logarithms  may  be 
used,  because  the  factor  for  converting  them  to  loge  (2.3025) 
cancels  in  the  ratio. 


CHAPTER  XVII. 

SILICON   AND    BORON. 

121.  Silica.    Mix  1  g.  of  finely  powdered  silica  with  4-5  g. 
of  anhydrous  sodium  carbonate.     Make  a  small  watch-spring 
spiral  on  the  end  of  the  platinum  wire,  and,  by  alternately  heat- 
ing in  the  Bunsen  flame  or  blast-lamp,  and  dipping  in  the  mix- 
ture, obtain  a  large  bead  and  heat  it  strongly  till  all  action  (?) 
seems  to  have  ceased.     Place  the  bead  in  a  test-tube  and  make 
others  by  the  same  process.     Dissolve  the  beads  in  a  small 
amount  of  water.     Add  hydrochloric  acid  a  drop  at  a  time 
until  the  solution  is  strongly  acid  (?).     Evaporate  the  solution 
to  dryness  on  the  sand  bath  (?).     Treat  the  residue  with  warm 
water,  wash  the  whole  contents  of  the  dish  into  a  test-tube,  and 
examine  (?). 

122.  Analysis  of  a  Silicate.     Mix  dry  potassium  carbonate 
with  anhydrous  sodium  carbonate  in  equal  proportions  in  a 
mortar.     Coil  the  platinum  wire  to  watch-spring  form.     Mix  a 
little  powdered  talc  (is  this  soluble  in  water?    What  is  its  com- 
mon name?)  with  6-7  times  as  much  of  the  "fusion  mixture," 
and  hold  some*  of  the  result  on  the  platinum  wire  in  the  flame  of 
the  blast-lamp  till  it  is  completely  melted  and  all  action  (?) 
has  ceased.     Repeat  till  several  beads  are  obtained.     Treat  the 
beads  with  boiling  water  in  a  test-tube  until  they  are  com- 
pletely disintegrated.     Filter  through  a  small  filter  paper  and 
wash  the  precipitate  with  water.     Preserve  this  filter  paper 
and  precipitate  for  use  later.     Acidify  the  filtrate  with  concen- 
trated hydrochloric  acid  and  proceed  as  in  121. 

Make  a  hole  in  the  paper  and  wash  the  precipitate  obtained 
above  into  a  test-tube.  Add  dilute  hydrochloric  acid,  and 
warm  (?).  Filter,  if  necessary,  and  add  ammonium  hydroxide 
to  alkaline  reaction  (?).  The  precipitate  is  aluminium  hydrox- 
ide. Boil  and  filter.  To  the  filtrate  add  a  few  drops  of  ammo- 
nium hydroxide,  some  ammonium  chloride  solution,  and  some 
sodium  phosphate  solution,  and  shake  (?).  Compare  106  c. 

123.  Silicon  Tetrafluoride.     Mix  intimately  1  g.  of  pulver- 
ized calcium  fluoride  with  an  equal  weight  of  sand,  place  in  a 
test-tube,  and  moisten    the    mixture  with    concentrated  sul- 
phuric acid.     Apply  a  gentle  heat  (?).     Hold  a  glass  rod,  with 
a  drop  of  water  at  its  lower  end,  in  the  gas  and  examine  the 
rod  (?). 


§  125]  SILICON  AND   BORON  99 

124.  Boric  Acid. 

a.  Pulverize  some  borax  and  make  a  strong  solution  in 
boiling  water.    Add  concentrated  hydrochloric  acid  until  the 
solution  is  strongly  acid,  and  set  aside  to  cool  (?).     Filter  off 
the  crystals,  wash  with  a  few  drops  of  cold  water  [Note  38, 
p.  85],  and  dry.     Dissolve  the  crystals  in  the  smallest  possible 
amount  of  boiling  water,  and  set  the  solution  aside  (?).     Filter, 
and  wash  the  crystals  as  before. 

b.  Dissolve  a  part  of  the  crystals  in  hot  distilled  water. 
Test  this  solution,  and  a  sample  of  the  distilled  water,  simulta- 
neously with  litmus  paper  (?).     Dip  a  strip  of  turmeric  paper 
in  the  same  solution,  wrap  it  round  the  upper  part  of  the  test- 
tube,  and  boil  the  solution  until  the  paper  is  dry  (?).    Touch 
the  paper  with  a  glass  rod  dipped  in  sodium  hydroxide  solu- 
tion (?).    This  is  a  test  for  boric  acid. 

Treat  the  rest  of  the  crystals  with  cold  sodium  hydroxide 
solution  (?). 

c.  Place  on  separate  parts  of  a  watch-glass  a  drop  of  concen- 
trated sulphuric  acid,  a  drop  of  glycerine,  and  a  very  little 
pulverized  borax.     Rub  the  end  of  a  platinum  wire  in  each  of 
these.     Bring  the  end  of  the  wire  slowly  up  to  the  outer  edge 
near  the  bottom  of  a  small  Bunsen  flame.     How  is  the  flame 
colored?    This  is  a  test  for  a  borate. 

An  alternative  method:  Dissolve  a  small  crystal  of  borax 
in  1-2  c.c.  of  water  in  a  test-tube.  Add  a  drop  or  two  of  con- 
centrated sulphuric  acid  and  then  2-3  c.c.  of  alcohol.  Heat 
the  mixture  and  set  fire  to  the  vapor  of  the  alcohol. 

125.  Borates. 

a.  Dissolve  1  g.  of  borax  in  distilled  water.  Test  both  this 
solution,  and  the  distilled  water,  with  litmus  paper  (?). 

Put  two  drops  of  the  solution  into  a  test-tube  and  dilute 
with  water  till  the  tube  is  two-thirds  full.  To  the  remainder 
add  silver  nitrate  solution  (?).  Add  silver  nitrate  solution  to 
the  very  dilute  solution  also  (?).  The  difference  is  more  marked 
if  the  dilute  solution  is  first  warmed.  For  comparison,  add 
silver  nitrate  solution  to  an  exactly  equally  diluted  sodium 
hydroxide  solution  (?).  What  conclusion  dp  you  draw  in 
regard  to  the  action  of  water  on  borax?  Write  the  equation, 
and  explain. 

6.  Heat  a  straight  platinum  wire  in  the  Bunsen  flame,  and, 
while  yet  glowing,  dip  it  into  a  small  quantity  of  borax.  Re- 
turn the  wire  to  the  flame  and  observe  the  changes  in  the  sub- 
stance (?)  until  it  forms  a  bead.  Try  borax  beads,  as  directed 
in  3  d,  e,  and  /,  with  cupric  oxide  (?),  manganese  dioxide  (?), 
and  ferric  oxide  (?),  separately. 


CHAPTER  XVIII. 

METALLIC    ELEMENTS    OP  THE   ALKALIES. 

126.   Potassium  Hydroxide. 

a.  Dissolve  about  30  g.  of  potassium  carbonate  [Notes  10, 
11,  12,  p.  2]  in  200-300  c.c.  of  water  in  a  large  beaker,  and 
heat  on  a  wire  gauze  to  boiling.  Slake  15-^0  g.  of  quicklime 
in  a  beaker  (?),  using  heat  if  necessary  to  start  the  action,  and 
make  the  product  into  a  very  thin  paste  with  water.  Add  this 
gradually,  and  with  constant  stirring,  to  the  boiling  solution  (?). 
Continue  boiling  for  a  few  minutes  (why?).  Let  the  mixture 
settle,  and,  when  it  is  cold,  decant  the  clear  liquid  (or  filter 
rapidly).  Use  the  solution  in  fy  c,  and  d. 

Is  calcium  hydroxide  appreciably  soluble  (Appendix  IV)? 
Is  calcium  carbonate  more  or  less  soluble  than  is  the  hydrox- 
ide? Formulate  the  action  and  explain  why  it  went  to  comple- 
tion. What  kind  of  hydroxides  alone  can  be  made  by  this 
method  [R  5531  ?  Which  hydroxides  are  of  this  kind  (Appendix 
IV)? 

6.  Find  the  strength  of  this  solution  by  titration  (alkali- 
metry). To  do  this,  place  a  carefully  measured  volume  (about 
10  c.c.)  of  the  clear  solution  in  a  small  flask.  Dilute  with 
about  four  times  its  volume  of  water,  as  the  concentrated 
solution  is  apt  to  decompose  the  indicator.  Fill  a  burette  with 
"normal"  [R  148]  hydrochloric  acid*  [Side-shelf],  Add  some 
phenolphthalein  solution  to  the  alkali  and  run  in  the  acid  cau- 
tiously until  the  red  color  just  disappears.  Note  the  volume 
of  acid  used.  Calculate  the  weight  of  potassium  hydroxide 
per  liter,  which  your  measurement  shows  to  be  contained  in 
the  alkaline  solution.  Express  this  also  in  terms  of  a  normal 
solution  containing  56  g.  of  KOH  per  liter  (for  example,  28  g. 
per  liter  would  be  0.5  normal). 

c.  (Two  students  working  together).  If  the  alkaline  solu- 
tion  is  above  normal,  calculate  the  volumes  of  water  and  of  the 
solution  required  to  make  100  c.c.  of  normal  alkali.  Place  the 
necessary  amount  of  water  (by  weighing)  in  a  100  c.c.  graduated 

*  Or  normal  oxalic  acid  may  be  prepared  (two  students  working 
together),  and  used  here.  Calculate  the  weight  of  pure  [Instructor] 
oxalic  acid  [R  499]  required  to  make  500  c.c.  of  normal  oxalic  acid 
solution  [R  148].  Weigh  out  [quant.]  this  amount  on  glazed  paper,  and 
transfer  it  to  a  500  c.c.  graduated  flask  [Storeroom].  Dissolve  the  acid 
in  distilled  water  and  then  fill  up  the  flask  to  the  mark. 

100 


§127]      ELEMENTS   OF  THE, ALKALIES 


101 


flask  [Storeroom]  and  fill  to  the  mirk  ton.th  ^the, 

the  solution  is  less  than  normal,  calculate  and  use  the  "amounts 

required  for  200  c.c.  of  semi-normal  alkali.) 

Measure  (burette)  5  c.c.  of  acetic  acid  into  a  flask  and  dilute 
with  about  20  c.c.  of  water  (or  take  25  c.c.  of  commercial  vine- 
gar), add  phenolphthalei'n,  titrate  with  the  normal  (or  semi- 
normal)  alkali,  and  calculate  the  percentage  of  acetic  acid 
present. 

d.  Place  very  small  quantities  of  the  following  solutions  in 
separate  test-tubes,  dilute  with  water,  and  add  excess  of  the 
solution  of  potassium  hydroxide  from  a  to  each;  ferric  chlor- 
ide (?) ;  cupric  sulphate  (?) ;  mercuric  chloride  (?).     Describe  the 
color  and  structure  of  the  precipitates  [Note  39,  below].     Boil 
the  contents  of  each  test-tube  (?).     Do  the  precipitates  dissolve 
or  change  in  any  way? 

What  kind  of  hydroxides  can  be  made  by  this  method?  Do 
any  metals  fail  entirely  to  form  hydroxides  [R  541]  ? 

e.  Pulverize  a  small  piece  of  potassium  hydroxide  and  leave 
it  exposed  to  the  air  on  a  watch-glass  for  24  hours,  or  more  (?). 
To  a  part  of  the  product  add  dilute  hydrochloric  acid   (?). 
Simultaneously,  treat  a  small  piece  of  sodium  hydroxide  in 
exactly  the  same  way  (?).     Compare  the  results  and  explain. 

Note  39.  —  The  structure  of  a  precipitate  may  be  described  as 
gelatinous,  flocculent,  curdy,  pulverulent,  granular,  or  crystalline. 
What  circumstances  will  determine  the  structure  of  a  precipitate? 
Hereafter,  describe  every  precipitate  by  terms  like  these. 

127.   Potassium  Nitrate. 

a.  Dissolve  25  g.  of  sodium  nitrate  and  22  g.  of  potassium 
chloride  in  50  c.c.  of  water  and  evaporate  to  half  the  volume 
on  the  sand  bath.  Fit  a  filter  paper  into  a  small  funnel  [Note 
24,  p.  9].  As  rapidly  as  possible  decant  the  hot,  clear  liquid 
from  the  crystals  and  set  it  aside.  Throw  the  crystals  which 
appeared  during  boiling  at  once  on  to  the  filter,  and  rapidly  press 
out  the  rest  of  the  mother-liquor  with  a  spatula.  Examine  the 
form  of  the  crystals  and  ascertain  what  they  are  (?).  (If  they 
are  too  small,  recrystallize  a  part  slowly  from  water  in  a  beaker 
in  order  to  learn  their  form.)  When  the  decanted  liquid  is  cold, 
press  the  product  on  a  filter  likewise.  Examine  this  set  of  crys- 
tals as  before  (?).  Compare  both  with  the  original  substances. 

To  understand  the  process,  note  the  solubilities  (grams  dis- 
solved bv  100  g.  water)  of  the  substances  concerned  (Appendix 
V): 

10°  100°  10°  100° 

Potassium  nitrate  246      Potassium  chloride 

Sodium  chloride  Sodium  nitrate 


102  ELBMEFTS   OF  THE   ALKALIES       [§  128 

Which  cf  these  substances  will  first  be  deposited  from  the 
boiling  liquid?  Ascertain  by  calculation  how  much  of  it 
(roughly)  will  be  deposited  at  100°,  how  much  more  will  come 
out  when  the  liquid  cools,  and  how  much  will  remain  in  the 
mother-liquor.  What  other  substance  will  be  present  in  large 
quantity  in  the  hot  mother-liquor,  and  how  much  of  it  must 
there  be?  How  much  of  this  product  will  be  deposited  when 
the  liquid  cools,  and  how  much  will  be  lost  by  remaining  dis- 
solved? What  per  cent  of  the  possible  yield  of  potassium 
nitrate  may  we  expect  to  get?  Dry  your  product,  weigh  it, 
and  calculate  what  per  cent  was  secured. 

Explain  why  purer  potassium  nitrate  can  be  obtained  by 
crystallizing  the  product  once  more  from  water. 

6.  Mix  intimately  in  the  mortar  5  g.  of  finely  pulverized 
potassium  nitrate  with  2  g.  of  charcoal,  and  drop  the  mixture  in 
small  portions  into  a  red-hot  crucible  (?).  What  gases  are 
evolved?  What  is  the  residue  (test  with  an  acid)? 

c.  Pulverize  5  g.  of  potassium  nitrate  and  mix  on  paper 
[CAUTION]  intimately  with  2  g.  of  flowers  of  sulphur.  Throw 
the  mixture  [Hood]  in  small  portions  into  a  red-hot  crucible  (?). 
What  gases  are  evolved?  Dissolve  the  residue  and  add  barium 
chloride  solution  (?).  Explain  the  explosive  power  of  gun- 
powder (?). 

128.  Potassium  Cyanide  [POISON].      How  is  this  salt  made 
[R  558]  ?    Place  2  c.c.   of  potassium  cyanide  solution  in  an 
evaporating-dish,  heat  it,  and  add  yellow  ammonium  sulphide 
solution  until  the  color  (?)  no  longer  disappears.     Evaporate  to 
complete  dryness  [Hood].     Dissolve  a  part  of  the  residue  with 
water,  and  add  ferric  chloride  solution  (?).     A  black  precipi- 
tate (?)  indicates  that  the  heating  was  not  sufficient.     If  this 
appears,  heat  the  residue  once  more  and  try  the  action  of  ferric 
chloride  again.     In  the   first  part  of  this  experiment,   what 
property  of  the  cyanides  [R  507Jf  and  which  kind  of  ionic  chem- 
ical change,  are  illustrated?    Is  this  change  instantaneous,  as 
is  the  union  or  disunion  of  ions? 

129.  Reactions  of  Potassium  Salts. 

a.  Heat  a  little  solid  potassium  nitrate  on  a  clean  platinum 
wire.     Notice  the  color  of  the  flame  and  examine  with  the 
spectroscope.      Make  a  diagram  showing  the  position  of  the 
lines  with  reference  to  the  D  line  (in  the  yellow),  which,  on 
account  of  the  sodium  present,  is  shown  by  all  flames  in  the 
laboratory. 

b.  Saturate    10  c.c.  of  warm   water  (40°)  with    potassium 
nitrate.     Add  this  solution  to  an  equal  volume  of  tartaric  acid 
solution  in  a  beaker  (?).     Agitate  and  cool  in  a  stream  of 


§131]       ELEMENTS   OF  THE  ALKALIES  103 

water  (?).  Note,  also,  the  effect  of  rubbing  the  inside  of  the 
vessel  with  a  glass  rod.  Describe  the  product  [Note  39,  p.  101]. 
Filter,  and  wash  the  precipitate  with  a  little  alcohol. 

c.  Dissolve  a  few  particles  of  the  precipitate  from  b  in  a 
drop  or  two  of  warm  water  and  test  with  litmus  (?).     Remem- 
bering that  tartaric  acid  is  a  dibasic  acid  (H2C4H406),  what  sort 
of  salt  must  the  product  be? 

To  a  few  particles  of  the  precipitate  add  dilute  hydrochloric 
acid  (?). 

To  a  part  of  the  precipitate  add  drop  by  drop  potassium 
hydroxide  solution  (shake  between  drops)  (?).  To  the  result- 
ing solution  add  concentrated  hydrochloric  acid  a  drop  at  a 
time.  Stir  vigorously  with  a  glass  rod,  and  cool  in  running 
water  between  drops  (?).  Finally,  try  the  effect  of  excess  of 
the  acid  (?). 

Heat  the  rest  of  the  precipitate  strongly  in  a  porcelain 
crucible  (?).  Extract  with  hot  water,  filter,  and  add  any  acid 
to  the  filtrate  (?).  The  ignition  of  all  potassium  or  sodium 
salts  of  organic  acids  gives  the  same  result. 

d.  Take  2-3  c.c.  potassium  chloride  solution,  and,  in  another 
test-tube,  dilute  a  few  drops  of  it  with  10  c.c.  of  water.    Then 
add  some  picric  acid  solution  to  each  portion  [Note  39,  p.  101]  (?). 
Explain  the  difference  in  behavior. 

What  substance  is  shown  to  be  present  in  a  solution  when  we 
get  the  tests  in  b  and  d? 

130.  Ammonium  Salts. 

a.  What  is  a  common  effect  of  heating  ammonium  salts 
(92  e)t    Heat  1  g.  of  ammonium  phosphate  in  a  hard  glass 
test-tube   (?).    Dissolve  the  residue  in  water  and  test  with 
litmus  paper  (?).     Is  simple  heating  a  test  for  an  ammonium 
salt?    Do  all  salts  of  ammonium  give  ammonia  when  heated 
(90  a;  98  a)?    Observe  the  odors  of  all  the  salts  of  ammonium 
(solids  and  solutions)  upon  the  side-shelf  (?),  and  explain. 

b.  Do  ammonium  salts  impart  color  to  the  flame? 

c.  Take  a  solution  of  any  ammonium  salt  and  divide  it  into 
three  portions.     To  one  add  excess  of  tartaric  acid  solution,  and 
shake  (?).    To  the  second  add  picric  acid  solution  (?).    Com- 
pare these  results  with  129  6  and  d.    To  the  third  add  sodium 
hydroxide  solution  and  note  the  odor  (?).    How  should  you 
distinguish  ammonium-ion  from  any  other  ionic  substance? 

d.  Test  ammonium  chloride  solution  with  litmus  (?).    Do 
ou  infer  that  ammonium  hydroxide  is  a  very  inactive  base 

535,  565]  ? 

131.  Sodium  Carbonate  by  Solvay  Process.    Take  75  c.c.  of 
ammonium  hydroxide,  dilute  with  25  c.c.  of  water,  and  dissolve 


104  ELEMENTS   OF  THE   ALKALIES        [§  132 

in  it  25  g.  of  powdered  ammonium  carbonate  by  shaking 
(ammonium  hydroxide  solution  is  used  instead  of  water  in 
order  to  secure  ultimately  a  higher  concentration  of  ammo- 
nium-ion than  could  be  obtained  with  the  carbonate  alone, 
the  solubility  of  this  salt  being  too  small).  Then  saturate  the 
solution  completely  with  sodium  chloride  by  prolonged  agita- 
tion with  finely  powdered  salt  in  a  corked  bottle.  If  crude  salt 
is  employed,  it  should  be  washed  with  water  before  use. 
Decant  the  clear  liquid  into  another  bottle,  fitted  with  cork  and 
two  tubes,  one  of  which  reaches  to  the  bottom.  If,  because  of 
delay,  a  dense  precipitate  has  appeared,  proceed  without  decant- 
ing. Through  the  latter  tube,  pass  in  carbon  dioxide  from 
the  laboratory  supply,  or  from  a  Kipp's  apparatus,  until  the 
solution  is  saturated.  This  operation  may  occupy  an  hour  or 
more.  During  the  absorption  of  the  carbon  dioxide,  the  exit 
tube  should  be  closed  to  prevent  waste  of  the  gas.  Close  the 
tubes  with  caps  of  rubber  tubing  plugged  with  glass  rods  and 
set  aside  over  night  (?).  Filter  off  the  deposit,  and  dry  by 
pressing  between  filter  papers. 

Dissolve  in  water  a  little  of  the  solid,  which  must  have  ceased 
to  smell  of  ammonia  (why?),  and  test  the  reaction  of  the  solu- 
tion with  litmus  (?).  If  the  solution  is  not  acid,  explain  why  it 
is  not  so. 

To  part  of  the  solid  add  any  dilute  mineral  acid  (?). 

Heat  the  rest  in  a  test-tube  clamped  so  that  the  mouth  is 
inclined  slightly  downward,  and  ascertain  what  gases  are 
evolved.  When  gas  ceases  to  be  given  off,  dissolve  the  cold 
residue  in  a  very  little  water,  test  the  reaction  of  the  solution 
with  litmus  paper  (?),  and  set  it  aside  to  crystallize  in  an  open 
dish  (?).  Explain  the  reaction  with  litmus  (?).  Dry  the 
crystals,  and  ascertain  the  effects  upon  them  of  (a)  addition  of 
an  acid  (?),  and  (b)  of  exposure  on  a  watch-glass  (?). 

Compare  the  solubilities  of  the  carbonate  (Appendix  IV) 
and  bicarbonate  of  sodium  [R  544],  and  explain  why  the  bicar- 
bonate is  made  first  and  then  the  carbonate  from  it. 

132.  Purification  of  Sodium  Chloride.  Prepare  about  150  c.c. 
of  a  cold  saturated  solution  of  common  salt  by  grinding  the 
salt  for  some  time  in  a  mortar  with  the  water.  If  crude  salt  is 
used,  it  must  first  be  washed  with  water.  Place  the  solution 
in  a  beaker,  and  pass  hydrogen  chloride  into  the  solution.  Pre- 
pare this  gas  by  placing  a  handful  of  common  salt  in  a  gen- 
erating-flask  (Fig.  11,  p.  29),  covering  it  with  concentrated 
hydrochloric  acid,  and  allowing  concentrated  sulphuric  acid  to 
fall  into  it  from  a  dropping-funnel.  The  hydrochloric  acid 
prevents  frothing  and  steadies  the  stream  of  gas  (why?). 


§  134]       ELEMENTS   OF  THE   ALKALIES  105 

Deliver  the  gas  into  the  solution  through  a  thistle-tube  with  the 
mouth  downward  (?).  When  considerable  precipitation  has 
occurred,  filter  by  putting  a  clean  silver  coin  with  milled  edges 
in  a  funnel,  pouring  the  liquid  and  crystals  upon  it,  and  press- 
ing with  a  spatula. 

Why  is  the  thistle-tube  preferable  to  ordinary  tubing? 

133.  Reactions  of  Sodium  Salts.    Take  some  salt  of  sodium 
and  try  the  flame  test,  and  examine  the  flame  with  the  spec- 
troscope as  in  129  a.    Take  a  solution  of  some  salt  of  sodium, 
and  add  to  one  portion  picric  acid  solution  (?),  and  to  the  other 
tartaric  acid  solution  (?).     Compare  all  the  results  with  those 
obtained  in  129  and  130  b  and  c.     How  could  you  distinguish 
sodium,  potassium,  and  ammonium  salts  from  one  another? 
How  could  you  demonstrate  positively  the  presence  both  of  a 
potassium  and  of  an  ammonium  salt  in  a  mixture  of  the  two 
(a)  with  and  (b)  without  the  aid  of  the  flame  test  or  spectroscope? 

Which  salts  of  potassium,  ammonium,  and  sodium  are  least 
soluble? 

134.  Ionic  Equilibrium  and  the  Ion-Product  Constant. 

o.  Dilute  a  few  drops  of  methyl  orange  solution  [R  355]  with 
much  distilled  water.  Add  a  few  drops  of  an  acid  (?)  and  then 
excess  of  a  base  (?).  What  colors  does  this  indicator  show  in 
neutral,  acid,  and  alkaline  solution,  respectively?  What  ionic 
substance  is  present  in  the  acid,  and  absent  from  the  other 
solutions? 

Take  three  portions  of  distilled  water  and  add  to  each  a  little 
methyl  orange  solution.  To  the  first  two  add  a  little  acetic 
acid  (?),  to  the  third  a  drop  of  hydrochloric  acid  (?).  To  the 
first  add  some  solid  sodium  chloride,  and  shake  (?).  To  the 
second  add  some  solid  sodium  acetate,  and  shake  (?).  What 
ionic  substance  has  disappeared?  Explain  the  difference  in 
behavior  [R  578].  To  the  third  add  solid  sodium  chloride,  and 
shake  (?).  Explain  the  absence  of  effect. 

In  what  way  did  63  b  illustrate  the  same  principle? 

b.  Take  three  portions  of  a  saturated  solution  of  potassium 
chlorate  in  as  many  test-tubes.     (If  there  is  any  deposit  in  the 
bottles,  this  and  the  following  solutions  must  be  shaken  before 
use  to  insure  saturation.)     To  the  first  add  saturated  sodium 
chloride  solution  (?),  to  the  second  saturated  potassium  chlor- 
ide solution  (?),  to  the  third  saturated  sodium  chlorate  solu- 
tion (?).    Allow  them  to  stand  fo~   a  minute  or  two   before 
drawing  any  conclusion.     Explain  [R  581].     The  experiments 
will  fail  if  all  the  solutions  are  not  saturated. 

c.  Explain  why,  in  132,  the  salt  is  precipitated.     If  the  crude 
salt  had  contained  other  salts,  which  of  them  would  have  been 


106  ELEMENTS   OF   THE   ALKALIES         [§  134 

affected  by  the  introduction  of  hydrogen  chloride,  and  which 
not?  Specifically,  would  sodium  sulphate  or  magnesium 
chloride  have  been  affected,  and  how?  If  either  of  these  would 
be  affected  and  had  been  present,  under  what  circumstances 
might  it  have  entered  into  the  precipitate  (Appendix  IV)? 
Within  what  limits,  then,  does  the  process  give  a  means  of 
purification? 

d.  To  1-2  c.c.  of  concentrated  hydrochloric  acid  add  con- 
centrated sulphuric  acid  drop  by  drop  (?).  Explain. 

Unknowns  (140)  may  be  introduced  at  this  point. 


CHAPTER  XIX. 

METALLIC    ELEMENTS    OF  THE   ALKALINE    EARTHS. 

136.  Calcium  Oxide.  Ignite  [Blast-lamp]  2-3  g.  of  broken 
marble  for  15  minutes  in  an  open  crucible,  placed  upon  the 
clay  triangle  (?).  Stir  occasionally  with  the  platinum  wire. 
When  cool,  add  a  little  water  (?).  Test  the  reaction  of  the 
liquid  towards  litmus  (?).  Has  water  any  effect  upon  marble? 
Now,  add  some  dilute  hydrochloric  acid  (?).  Compare  this 
with  the  action  of  the  acid  upon  marble  (109  6). 

How  may  the  decomposition  of  the  marble  be  arrested  (?) 
and  reversed  (?)  without  altering  the  temperature?  What 
conditions  permitted  complete  decomposition  to  take  place 
here? 

136.  Calcium  Hydroxide.     Slake  a  piece  of  calcium  oxide 
and  shake  the  product  with  half  a  liter  of  distilled  water;  let  the 
solution  settle,  or  filter  rapidly,  and  use  the  clear  liquid. 

a.  Blow  air  from  the  lungs  by  means  of  a  tube  through  a 
part  of  the  lime-water  (?).  How  could  you  determine  the 
proportion  of  carbon  dioxide  in  a  sample  of  air? 

6.  Dilute  the  remainder  of  the  lime-water  with  an  equal 
volume  of  distilled  water,  and  pass  a  stream  of  carbon  dioxide 
from  the  laboratory  supply,  or  from  a  Kipp's  apparatus,  per- 
sistently through  the  solution  (?).  Boil  a  part  of  the  resulting 
clear  liquid  (?).  Explain.  Describe  all  precipitates  [Note  39, 
p.  101],  both  here  and  in  all  succeeding  experiments.  Why 
does  the  second  precipitate  appear  to  differ  in  quantity  from 
the  first?  What  is  "temporary  hardness"  in  water  [R  594]  ? 

137.  Reactions  of  Calcium  Salts.    Diluted  calcium  chloride 
solution  [Note  40,  below]  may  be  used  for  b,  c,  d,  and  /. 

a.  Try  the  flame  test  and  examine  with  the  spectroscope 
(see  that  the  platinum  wire  is  clean.    Note  41,  below).     Make 
a  sketch  of  the  spectrum  showing  the  positions  of  the  lines 
with  reference  to  the  sodium  and  potassium  lines. 

b.  To  a  part  of  the  solution  containing  calcium-ion  add 
ammonium  oxalate  solution  in  excess  (?).     Filter  off  the  pre- 
cipitate and  divide  it  into  two  parts.     Place  each  part  in  a  test- 
tube,  and  treat  one  with  dilute  hydrochloric  acid  (?)  and  the 
other  with  diluted  acetic  acid  (?).    Explain  this  difference  in 
behavior  towards  hydrogen-ion  [R  598].    Why  was  ammo- 
nium oxalate  used  in  preference  to  oxalic  acid? 

107 


108        ELEMENTS  OF  ALKALINE  EARTHS   [§  137 

c.  To  the  second  portion  of  the  solution  containing  calcium- 
ion  add  ammonium  carbonate  solution  (?).    Warm,  if  necessary. 
Filter,  divide  the  precipitate  and  treat  parts  of  it  with  hydro- 
chloric acid  (?)  and  diluted  acetic  acid  (?)  respectively.     Ex- 
plain the  result.     Explain  also  the  difference  in  behavior  of  the 
oxalate   and   the   carbonate   of   calcium  towards  acetic   acid, 
taking  account  both  of  the  solubilities  of  these  salts,  and  of  the 
fundamental  difference  in  behavior  between  oxalic  and  carbonic 
acids. 

d.  To  the  third  portion  of  the  solution  add  excess  of  dilute 
sulphuric  acid  (?).     Filter  and  divide  the  clear  (if  not,  filter 
again)   nitrate  into  three  parts   (reserve  one  for  e).     To  one 
small  part  add  an  equal  volume  of  alcohol  (formation  of  all 
precipitates,  if  long  delayed,  may  be  hastened  by  vigorous 
stirring)  (?). 

Neutralize  (test?)  the  second  portion  with  ammonium  hy- 
droxide (why?),  add  ammonium  oxalate  solution  (?),  and 
explain.  Is  the  sulphate  or  the  oxalate  of  calcium  more  soluble? 
Confirm  your  inference  by  giving  the  solubilities  (Appendix 
IV). 

e.  What  is  "permanent  hardness"  in  water  [R  595]  ?    Boil 
the  third  portion   of  the  filtrate  from  d   (?).     Compare  the 
result  with  that  in  136  b.     Add  now  a  little  sodium  carbonate 
solution  (?).     Is  the  carbonate  or  the  sulphate  of  calcium  more 
soluble?    What  are   their  actual  solubilities?    How  may  per- 
manent hardness  be  removed?    What  is  one  objection  to  the 
presence  of  hardness  in  a  domestic  water  supply  (119  b,  last  par.)  ? 

/.  To  the  fourth  portion  of  the  solution  containing  calcium- 
ion  add  some  dilute  hydrochloric  acid,  mix,  and  then  add 
ammonium  oxalate  solution  (?).  Explain  [R  601].  If  any 
precipitate  appears,  add  more  hydrochloric  acid.  Now  add  a 
large  amount  of  sodium  acetate  solution  (?).  What  is  the 
precipitate  (calcium  acetate  is  soluble),  and  why  is  it  formed 
[R  601,  650]  ? 

Note  40.  —  In  this  and  all  following  paragraphs  headed  "reac- 
tions," where  "diluted"  solutions  are  spoken  of,  the  solutions  on 
the  side-shelf  must  be  diluted  with  3-4  volumes  of  distilled  water 
to  secure  good  results. 

Note  41.  — After  use,  the  platinum  wire  must  be  cleaned.  Form 
upon  it  a  borax  bead,  and  cause  the  molten  bead  to  traverse  the 
wire  from  end  to  end  several  times.  Throw  off  the  bead.  Heat 
the  wire  persistently  in  the  Bunsen  flame,  dipping  it  from  time  to 
time  in  hydrochloric  acid  (why?),  until  the  wire  no  longer  colors 
the  flame.  If  much  corroded,  the  wire  may  be  boiled  in  nitric 
icid  before  being  heated. 


§  140]   ELEMENTS  OF  ALKALINE  EARTHS        109 

138.  Reactions  of  Strontium  Salts.    Use  diluted  [Note  40] 
strontium  chloride  solution  for  6,  c,  and  d. 

a.   Same  as  137  a. 

6.   Add  ammonium  carbonate  solution  (?). 

c.  Add  dilute  sulphuric  acid  (?). 

d.  Add  a  clear  solution  of  calcium  sulphate  (made  by  shak- 
ing a  little  of  the  pulverized  salt  with  distilled  water  and  filter- 
ing until  clear)  (?).    The  precipitate  may  come  slowly.     Explain. 

139.  Reactions   of   Barium   Salts.     Use   diluted  [Note   40] 
barium  chloride  solution  for  6,  c,  and  d. 

a,  b,  c.     Same  as  138  a,  b,  c. 

d.  Add  a  clear  solution  of  strontium  sulphate  (made  by 
shaking  the  salt  with  distilled  water  and  filtering)  (?).  Explain. 

Compare  with  138  d,  and  arrange  the  sulphates  of  these  three 
metals  in  the  order  of  solubility.  Give  two  methods  of  dis- 
tinguishing the  compounds  of  the  elements  in  this  family. 
Examine  the  table  of  solubilities  (Appendix  IV)  and  suggest 
another  way  of  distinguishing  the  three  members,  and  one  way 
of  distinguishing  calcium-ion  and  barium-ion,  respectively, 
from  the  other  two.  How  could  you  tell  a  solution  containing 
the  ions  of  a  member  of  this  family  from  one  containing  those 
of  the  members  of  the  previous  family? 

140.  Identification   of   Unknown   Substances.    Take   three 
dry  test-tubes,  apply  to  the  instructor  for  three  "unknown" 
substances,  and  ascertain  by  the  use  of  any  experiments  you  can 
devise  what  each  is. 

a.   Study:  (1)  Physical  appearance  (?). 

(2)  Odor  (?). 

(3)  Solubility  in  water  and  reaction  of  the  solution  toward 
litmus  (?).     Use  this  aqueous  solution,  and  employ  the  reac- 
tions of  the  metallic  ions  just  studied,  for  the  purpose  of  recog- 
nizing the  positive  radical.     If  the  substance  is  insoluble  in 
water,  try  dilute  hydrochloric  acid. 

(4)  Effect  of  heating  in  a  dry  test-tube  (?).     Observe  closely 
the  behavior  of  the  substance,  and  try  to  identify  the  vapors 
or  gases  given  off.    Preserve  the  residue,  as,  after  the  next 
experiment,  examination  of  this  may  be  necessary. 

Before  trying  this  experiment,  make  a  list  of  afl  the  negative 
radicals  known  to  you,  and  place  opposite  to  each  the  gases,  if 
any,  which  salts  containing  that  radical,  when  heated,  might 
be  expected  to  give  off.  Consider  also  the  means  of  recognizing 
these  gases,  if  formed. 

(5)  Heating  with  a  drop  or  two  of  concentrated  sulphuric 
acid  (?). 


110        ELEMENTS  OF  ALKALINE  EARTHS    [§  140 

Before  trying  this  experiment,  add  to  the  above  list  the  reac- 
tions of  sulphuric  acid  with  salts  containing  each  of  the  negative 
radicals.  Consider  also  the  means  of  recognizing  such  of  the 
possible  products  as  are  volatile. 

(6)  Heating  the  residue   from  (4)   with   concentrated   sul- 
phuric acid,  or  such  other  confirmatory  experiments  with  this 
residue  as  the  results  of  (4)  and  (5)  suggest  (?). 

(7)  Other  experiments  suggested  by  the  results  of  (l)-(6). 

b.  Write  out  the  experiments  and  reasoning  carefully  in 
your  note-book,  and  make  sure  that  they  prove  the  substance 
to  be  the  one  you  finally  decide  that  it  is,  and  exclude  the  pos- 
sibility of  its  being  any  other.  Report  the  result  to  the  in- 
structor. 


CHAPTER  XX. 

COPPER  AND   SILVER. 

141.  Cuprous  Chloride. 

a.  Dissolve  about  2  g.  of  cupric  chloride  in  15  c.c.  of  water 
in  a  small  flask.  Add  2-3  c.c.  of  pure,  concentrated  hydro- 
chloric acid  and  about  5  g.  of  copper  nails,  and  boil  [Hood] 
until  the  green  tint  is  no  longer  perceptible  in  the  dirty  yellow- 
ish-brown color  of  the  product.  If  a  few  drops  added  to  a  test- 
tube  full  of  water  confer  a  blue  tinge  upon  the  water,  the  action 
is  still  incomplete.  What  ion  confers  the  blue  tinge?  What 
change  do  the  cupric  ions  undergo?  Is  the  change  an  oxidation 
or  a  reduction  of  cupric  chloride? 

6.  To  a  small  part  of  the  solution,  when  cold,  add  excess  of 
sodium  hydroxide  solution  (?).  Why  is  so  much  of  this  re- 
quired? Preserve  the  mixture  in  a  corked  test-tube  for  use 
in  143. 

c.  Pour  the  rest  of  the  solution  from  a  into  a  large  amount  of 
water  in  a  beaker   (?).     Expose  some  of  the  product,  while 
covered  with  water,  to  the  sunlight  (?). 

d.  To  the  rest  of  the  product  from  c  add  concentrated  hydro- 
chloric acid,  and  shake  (?).     What  is  the  complex  negative  ion 
here  formed  [R  621]?     Does  it  give  a  greater  or  a  less  concen- 
tration of  cuprous-ion  than  does  the  insoluble  cuprous  chlor- 
ide?   Upon  this  basis  explain  the   process  of  solution  here 
observed.     Pour  a  little  of  the  solution  into  much  water  (?). 

e.  To  the  rest  of  the  solution  made  in  d  add  a  little  concen- 
trated nitric  acid  (?).     What  ionic  substance  is  shown  by  its 
color  to  be  present?    Pour  this  solution  into  much  water  (?). 
Consider  each  ionic  substance  originally  present  in  the  solution, 
and  explain  how  it  is  affected  by  the  nitric  acid. 

Define  this  form  of  oxidation,  and  the  form  of  reduction  in  a, 
in  terms  of  the  hypothesis  of  ions. 

142.  Cupric  Hydroxide. 

a.  To  1-2  c.c.  of  diluted  cupric  sulphate  solution  add  excess 
of  sodium  hydroxide  solution  (?).    Take  one-third  of  this  mix- 
ture and  boil  it  (?). 

b.  Boil  1  g.  of  sugar  dissolved  in  water  (or  diluted  glucose 
syrup)  with  a  few  drops  of  dilute  sulphuric  acid  for  several 
minutes  (?).    This  gives  glucose  and  levulose  [R  500].    Add 

111 


112  COPPER  AND   SILVER  [§  143 

this  glucose  solution  to  another  portion  of  the  mixture  from  a, 
warm  gently  (?),  and  note  all  changes. 

c.  To  the  remainder  of  the  mixture  from  a  add  ammonium 
hydroxide,  and  shake  (?).  What  complex  ion  possesses  this  blue 
color  [R  623,  625]  ?  Does  this  ion  give  a  greater  or  a  less  con- 
centration of  cupric-ion  than  does  the  insoluble  hydroxide? 
Upon  this  basis  explain  the  process  of  solution  here  observed. 

143.  Cuprous  Oxide.     Divide  the  mixture  from  141  b,  con- 
taining a  precipitate  of  hydrated   cuprous  oxide,  into  three 
parts. 

a.  Shake  one  persistently  with  air  in  a  bottle,  admitting 
fresh  air  from  time  to  time  (?). 

6.  Boil  the  second  portion  (?). 

c.  To  the  third  portion  add  ammonium  hydroxide  (?).  What 
is  the  color  of  the  mixture?  What  complex  ion  is  formed 
[R  622]?  Why  is  cuprous  oxide  dissolved  by  ammonium 
hydroxide  solution? 

Shake  this  solution  with  air.  What  ion  is  formed?  Is  the 
action  more  or  less  rapid  than  in  a,  and  why? 

144.  Cuprous  Iodide.     Dilute  a  few  drops  of  cupric  sulphate 
solution  and  add  potassium  iodide  solution  (?).     Filter.     Wash 
the  precipitate  [Note  38,  p.  85]  (?).    Add  part  of  the  filtrate  to 
some  starch  emulsion  (?).     Shake  the  rest  with  some  chloro- 
form (?).    Read  the  footnote  to  p.  11. 

145.  Reactions  of  Cupric  Salts.    Use  diluted  cupric  sulphate 
solution.    What  is  the  color  of  cupric  sulphate  itself?    To 
what  is  the  color  of  the  solution  due? 

a.  Test  the  reaction  of  the  solution  with  litmus  paper  (?) 
and  explain  [R  536,  344].     Is  copper  an  active  metallic  ele- 
ment? 

b.  Lead  hydrogen  sulphide  through  another  portion  (?).    Is 
this    action    reversible,    theoretically?    Add    dilute    sulphuric 
acid  (?).     Do  dilute  acids  act  upon  any  sulphides  (74  g)1    Why 
not  upon  this  one  [R  600]  ? 

c.  To  another  portion  add  potassium  ferrocyanide  solution 
[R  536]  (?). 

d.  Note  here  the  interaction  (68  a)  of  zinc  with  cupric-ion  (?). 

e.  Make  a  borax  bead  and  heat  with  it  a  minute  particle  of 
cupric  oxide  in  the  oxidizing  (?)  and  in  the  reducing  (?)  flame, 
as  in  3  e.     The  latter  requires  patience.     If  cupric  sulphate  had 
been  used  here,  what  reaction  would  have  taken  place  [R  390]? 

/.  Prepare  a  match  (or  splinter  of  wood)  as  in  86.  Place  on 
the  end  a  moistened  mixture  of  any  copper  salt  with  anhydrous 
sodium  carbonate  and  heat  in  the  reducing  region  of  a  small 
Bunsen  flame.  Break  up  the  charred  stick  gently  in  water  in 


§  149]  COPPEE  AND   SILVER  113 

a  mortar,  wash  away  the  lighter  particles,  and  examine  the 
residue  (?). 

146.  Ammonio-cupric  Compounds.    To  a  diluted  solution  of 
cupric  sulphate  add  ammonium  hydroxide  (?),  first  a  drop  or 
two  (?),  then  in  excess  (?).     Of  what  ion  does  the  copper  now 
form  a  part?    Do  other  compounds  of  copper  yield  the  same 
ion    (142  c)?    Which  action  of  all  those  in  146  and  146  should 
you  hold  to  give  the  most  delicate  test  for  cupric-ion? 

Try  with  the  blue  solution  the  tests  in  146  6,  c,  and  d  (?) . 
Are  the  concentrations  of  cupric-ion  given  by  cupric  sulphide  (?), 
cupric  ferrocyanide  (?),  cupric  sulphate  (?),  and  cupric  hydrox- 
ide (?),  larger  or  smaller  than  the  concentration  of  free  cupric- 
ion  given  by  ammonio-cupric-ion?  Which  of  these  compounds 
would  be  dissolved  by  ammonium  hydroxide  solution,  and 
which  not? 

147.  Guprocyanides.    To  a  diluted  solution  of  cupric  sul- 
phate add  potassium  cyanide   solution  [CARE!    POISON],  first 
a  drop  or  two  (?),  then  in  excess  (?).     Does  the  solution  show 
the  color  of  cupric-ion?    In  what  form  of  "combination  is  the 
copper  [R  624]  ?    Divide  the  solution  into  three  parts  and  try 
the  tests  for  cupric-ion  given  in  146  b  and  d  (?).     Would  cupric 
sulphide  dissolve  in  potassium  cyanide  solution?    Explain  your 
answer.    To  the  third  portion  add  ammonium  .hydroxide  (?). 
Do  cupric  sulphide  (?)  and  ammonio-cupric-ion  (?)  give  larger 
or  smaller  concentrations  of  free  copper  ions  than  does  the 
cuprocyanide?    Would  potassium  cuprocyanide  give  the  bead 
test  (146  e)  or  the  match  test  (146  /)? 

148.  Double  Salts  (Potassmm-Cupric  Sulphate). 

a.  Saturate  water  at  70°  with  5  g.  of  finely  powdered  potas- 
sium sulphate  (about  25  c.c.  will  be  required).     Calculate  the 
weight  of  crystallized  cupric  sulphate  which  must  be  taken  to 
get  an  equimolecular  proportion,  and  dissolve  it  in  its  own 
weight  of  hot  water.     Mix  the  two  solutions,  taking  care  not  to 
allow  any  undissolved  fragments  of  either  salt  to  get  into  the 
mixture,  and  set  the  result  aside  to  crystallize  (?).      Examine 
the  form  of  the  crystals  and  compare  with  those  of  blue  vit- 
riol (?).     Dissolve  a  part  of  the  crystals  in  water  and  use  por- 
tions of  the  solution  for  b. 

b.  With  the  solution  try  tests  in  145  b,  c,  and  d  (?).     Is  cupric- 
ion  present?    To  another  portion  add  ammonium  hydroxide  (?). 

How  do  double  salts  differ  (a)  from  complex  compounds  like 
potassium  cuprocyanide  and  ammonio-cupric  sulphate  and  (b) 
from  simple  salts  like  cupric  sulphate? 

149.  Equivalent  of  Copper  [Quant.].    Take  a  small  rod  of 
pure  zinc,  smooth  the  ends  with  a  file,  and  weigh  carefully. 


114  COPPER   AND    SILVER  [§  150 

Place  in  a  beaker  an  exactly  known  weight  of  crystallized 
cupric  sulphate  (about  2  g.),  and  dissolve  in  distilled  water. 
Put  the  zinc  in  this  solution,  and  allow  them  to  remain  in  con- 
tact until  the  latter  is  completely  decolorized.  Remove  the 
zinc,  free  it  carefully  from  the  brown  deposit  (?),  and  dry  and 
weigh  it.  What  weight  of  zinc  has  gone  into  solution? 

To  avoid  weighing  the  precipitate  of  copper,  which  it  would 
be  difficult  to  do  exactly,  calculate  from  the  formula  what 
quantity  of  copper  was  contained  in  the  amount  of  blue  vitriol 
taken  (?).  Calculate  from  your  data  the  weight  of  copper  dis- 
placed by  the  equivalent  weight  of  zinc  found  in  35  b  or  36  a,  or, 
if  zinc  was  not  then  employed,  assume  the  latter  to  be  32.7. 
This  weight  of  copper  will  be  the  equivalent  (that  of  oxygen 
being  8).  Look  up  the  specific  heat  of  copper  (Appendix  III), 
and  use  this  and  the  equivalent  observed  to  find  the  atomic 
weight  (?). 

What  other  atomic  weights  could  be  measured  on  this  plan? 

150.   Reactions  of  Silver  Salts. 

a.  Take  1-2  c.c.  of  silver  nitrate  solution.     Test  its  reaction 
towards  litmus  [R  536].  (?).     Is  silver  more  or  less  active  as  a 
metallic  element  than  copper? 

Add  dilute  hydrochloric  acid  until  no  further  precipitation 
occurs  (?)'.  Filter,  wash  the  precipitate  with  water,  and  place 
a  small  part  of  it  in  the  sunlight  (?). 

What  effect  does  the  skin  have  on  silver  nitrate? 

b.  To  a  small  part  of  the  precipitate  add  ammonium  hydrox- 
ide (?).    What  complex  ion  is  formed  ?     Now  add  dilute  nitric 
acid  in  excess  (?).     Formulate  the  action  of  this  acid. 

c.  To  another  small  part  add  sodium  thiosulphate  solution  (?)„ 
Pass  hydrogen  sulphide   (see  /)  through  the  solution  (?).     Ex- 
plain both  actions. 

d.  Place  the  rest  of  the  precipitate  in  a  porcelain  crucible, 
put  on  it  a  piece  of  granulated  zinc,  and  fill  up  with  dilute  sul- 
phuric acid.     Stir  from  time  to  time  (?).     After  an  hour  or  two 
pour  off  the  acid,  take  out  any  unchanged  zinc,  wash  the  pre- 
cipitate with  water  by  decantation,  add  ammonium  hydroxide, 
and  filter.     Find  out  whether  any  silver  chloride  had  remained 
unchanged  and  so  passed  into  the  filtrate  (150  6)  (?).     When 
the  filter  paper  is  dry,   place  the  dark  powder  in  a  hollow  on  a 
stick  of  charcoal  and  melt  it  with  the  flame  of  the  blast-lamp 
directed  downward  upon  it  (?). 

e.  Dilute  a  few  drops  of  silver  nitrate  solution  and  divide 
into  two  parts.    To  one  add  potassium  bromide  solution  (?), 
and  to  the  other  potassium  iodide  solution  (?).     Add  to  each 
some  ammonium  hydroxide  (?).     Compare  the  rates  of  action 


§  150]  COPPER  AND  SILVER  115 

with  that  on  silver  chloride  (?).  Arrange  the  three  salts  and 
ammonio-argentic-ion  in  the  order  of  decreasing  ability  to  give 
argentic-ion  (?).  Relate  this  order  to  that  of  solubility  (Appen- 
dix IV). 

/.  Dilute  2-3  drops  of  silver  nitrate  solution  and  lead  in 
hydrogen  sulphide  (?).  Is  this  action  reversible,  theoretically? 
Divide  the  product  into  two  parts,  and  to  one  add  dilute  nitric 
acid  (?). 

To  the  other  part  add  potassium  cyanide  solution  [CAUTION! 
POISON]  (?).  What  is  formed?  Could  silver  chloride  be  pre- 
cipitated from  this  solution  (64  6)?  Explain. 

g.  To  1  c.c.  of  silver  nitrate  solution  add  a  few  drops  of 
potassium  dichromate  solution  (?).  Test  the  solutions  before 
(?)  and  after  mixing  (?)  with  Congo  red  paper  [R  355].  (If 
the  color  of  the  dichromate  obscures  that  of  the  Congo  red, 
wash  the  test-paper  with  distilled  water.)  What  product  does 
this  show?  Make  the  equation  accordingly. 


CHAPTER  XXI. 

MAGNESIUM,   ZINC,    CADMIUM,   MERCURY. 

161.  Magnesium.     Mix  thoroughly  in  a  mortar  equal  bulks 
of  magnesium  powder  and  powdered  calcium  carbonate.     Put 
the  mixture  in  a  test-tube  (it  should  fill  about  half  an  inch  of 
the  tube),  fix  the  tube  in  a  clamp  on  the  stand,  and  heat  the 
top  layer  in  the  Bunsen  flame  until  the  reaction  begins.     Be 
careful  to  keep  the  tube  directed  away  from  the  face  during  the 
heating.     Allow  the  test-tube  to  cool,  add  a  little  water,  and 
then,  slowly,  an  excess  of  concentrated  hydrochloric  acid  (?). 
(If  the  tube  has  been  broken,  place  the  contents  with  the  acid 
in  a  beaker.)     What  effect  will  the  acid  have  upon  any  excess 
of  either  of  the  ingredients?    The  acid  will  also  dissolve  the 
oxides  of  magnesium  and  calcium  formed  by  the  action.     When 
all  action  has  ceased,  filter  and  wash  the  black  residue  (?)  with 
water.     After  drying  this  on  the  radiator  or  water  bath,  prove 
that  it  is  carbon.    This  may  be  done  by  placing  some  of  it  in  a 
dry  test-tube,  adding  a  pinch  of  potassium  chlorate,  heating  in 
the  Bunsen  flame,  and  pouring  the  gas  when  it  has  cooled  (close 
the  tube  with  the  thumb  while  waiting  for  this)  into  a  test- 
tube  containing  2  c.c.  of  lime-water,  and  shaking  (?). 

What  is  the  reducing  agent  in  this  action? 
Examine  the  test-tube  (?)  and  explain  [R  518].    . 

162.  Properties  of  Magnesium  Compounds. 

a.  Try  whether  magnesium  chloride  dissolves  completely  in 
water  (?).     Test  the  solution  with  litmus  (?). 

Heat  some  of  the  crystals  strongly  in  a  dry  test-tube  (?). 
Test  the  reaction  towards  litmus  paper  of  the  water  which  con- 
denses in  the  tube  (?),  and  then  remove  the  liquid  from  the 
sides  of  the  tube  with  a  piece  of  filter  paper.  Does  the  residue 
dissolve  in  water?  Explain. 

b.  To  some  diluted  magnesium  sulphate  solution  add  ammo- 
nium hydroxide  (?).     Explain  the  result  in  terms  of  the  ion- 
product  constant  [R  587]  (?).     Now  mix  with  some  ammonium 
hydroxide  several  times  its  volume  of  ammonium  chloride  solu- 
tion (what  effect  will  this  have  on  the  ionization  of  ammonium 
hydroxide?    Would  ammonium  sulphate  answer  as  well?),  and 
then  add  the  mixture  to  a  new  portion  of  magnesium  sulphate 
solution  (?).     Explain  in  terms  of  the  ion-product  constant. 

To  this  combination  of  three  solutions  add  sodium  phosphate 

116 


§  153]        MAGNESIUM,   ZINC,   MERCURY  117 

solution  (see  106  c)  (?).      Explain  the  purpose  of  each  ingre- 
dient. 

c.  To  a  fresh  portion  of  the  diluted  magnesium  sulphate 
solution  add  ammonium  carbonate   solution,  and  warm    (?). 
Repeat,  adding  excess  of  ammonium  chloride  solution  to  the 
magnesium  sulphate  solution  before  using  the  carbonate  (?). 

Calcium-ion  (137  c),  strontium-ion  (138  6),  and  barium-ion 
(139  6)  were  also  precipitated  by  ammonium  carbonate. 
Repeat  these  experiments  with  them,  adding  first  excess  of 
ammonium  chloride  solution  (?).  If  you  had  a  salt  of  magne- 
sium mixed  with  a  salt  of  one  of  those  other  metals,  how  should 
you  proceed  so  as  to  precipitate  a  compound  of  the  alkaline 
earth  metal  first  and  one  of  magnesium  afterwards? 

Add  two  drops  of  hydrochloric  acid  (why?)  to  about  250  c.c. 
of  the  city  water,  evaporate  to  small  bulk,  and  test  it  for  cal- 
cium-ion and  magnesium-ion. 

d.  Pass   hydrogen    sulphide    through   magnesium    sulphate 
solution  (?). 

153.  Reactions  of  Zinc  Salts.  Use  diluted  zinc  sulphate 
solution. 

a.  Test  the  solution  with  litmus  paper  (?).     Explain. 

6.  To  a  part  of  it  add  sodium  carbonate  solution  (?),  at  first 
a  little  and  then  in  excess.  Note  the  gas  evolved  (?).  Why  is 
the  gas  slow  in  appearing?  Relate  this  result  to  that  in  a  (?). 
Bring  the  contents  of  the  tube  to  the  boiling-point,  filter,  and 
wash  the  precipitate  with  water.  To  a  portion  of  the  precipi- 
tate add  an  acid  (?).  Account  for  the  evolution  of  gas  during 
the  precipitation.  Dry  the  rest  of  the  precipitate  for  c. 

c.  Heat  the  dried,  basic  zinc  carbonate  from  b  in  a  porcelain 
crucible  to  redness  for  a  few  minutes.     Remove  a  small  portion 
of  the  product  and  try  the  action  of  an  acid  upon  it  (?).     If  it 
effervesces,  ignite  for  a  longer  time.     What  is  the  color  of  the 
product  when  hot,  and  when  cold?    Reserve  for  d. 

d.  Moisten  the  residue  from  c  with  a  few  drops  of  a  cobalt 
chloride  solution  and  heat  again  (?). 

e.  To  another  part  of  the  zinc  sulphate  solution  add  a  very 
little  sodium  hydroxide  solution,  and  shake  (?).     Filter,  sus- 
pend the  precipitate  in  water,  and  divide  into  three  parts.     To 
one  add  an  excess  of  sodium  hydroxide  solution  (?).     Does  this 
show  zinc  hydroxide  to  be  basic,  or  acidic?    To  the  second  por- 
tion add  dilute  hydrochloric  acid  (?).     What  sort  of  hydroxide 
does  it  now  seem  to  be?    Explain  [R  648]. 

To  the  third  portion  add  ammonium  hydroxide  (?).     What 
complex  ion  is  formed  [R  648]  ? 
/.  To  a  third  portion  of  zinc  sulphate  solution  add  ammo- 


118  MAGNESIUM,   ZINC,   MERCURY        [§  154 

nium  sulphide  solution  (?).     Filter,  and  preserve  the  precipi- 
tate for  g. 

g.  Roll  up  a  small  part  of  the  filter  paper  from  /  into  a  ball, 
and  coil  the  platinum  wire  tightly  round  it.  Roast  the  whole 
in  the  Bunsen  flame  (?).  Moisten  the  ash  with  cobalt  chloride 
solution  and  heat  again  (?). 

154.  Relative  Activity  of  Several  Acids.     In  clean  test-tubes 
place  equal  volumes  of  (1)  zinc  chloride,  (2)  zinc  sulphate,  and 
(3)   zinc  acetate  solutions.     Compare  their  reactions  towards 
litmus  and  towards  Congo  red  paper  [R  356]  (?).     Into  each 
pass  hydrogen  sulphide  to  saturation  (test?  Note  36,  p.  67)  (?). 
Are   actions  like   this   reversible,   theoretically?    The   reverse 
action  consists  in  the  action  of  what  acid  upon  what  insoluble 
salt  in  each  case?    Will  it  be  equal  with  different  acids  [R  599]? 
If  not,  the  most  active  acid  will  have  kept  the  most  zinc  in  solu- 
tion and  the  least  active  the  least.     To  ascertain  how  much 
zinc  remains  in  each  solution,  filter  the  mixtures  separately,  and, 
after  testing  with  Congo  red  paper  (?),  add  ammonium  hydrox- 
ide to  each  (?).     The  precipitates   are  zinc  sulphide   (why?), 
Compare  the  amounts  (?).     Infer  the  relative  activities  of  the 
acids  (?). 

Confirm  the  conclusion,  roughly,  by  putting  some  of  the 
precipitate  into  each  of  three  test-tubes,  treating  directly  with 
dilute  hydrochloric,  sulphuric,  and  acetic  acids,  of  equivalent 
concentrations,  and  comparing  the  rates  of  action  (?). 

Why  was  ammonium  sulphide  used  in  153  /  ? 

155.  Ionic  Equilibrium.     Take  a  larger  amount  of  zinc  sul- 
phate solution,  and  add  sulphuric  acid  to  it  cautiously  until  a 
sample  just  ceases  to  give  any  precipitate  with  hydrogen  sul- 
phide.    Explain.     Now  add  much  powdered,  anhydrous  sodium 
sulphate,  stir  until  it  has  dissolved,  and  test  a  part  with  hydro- 
gen sulphide  again  (?).    What  effect  must  the  great  addition  of 
sulphate-ion  have  upon  the  hydrogen-ion  introduced  by  the 
sulphuric  acid?    Why  is  zinc  sulphide  now  precipitated? 

156.  Reactions   of   Cadmium   Salts.     Use  diluted  cadmium 
sulphate  solution. 

a.  Same  as  153  e.     Answer  the  same  questions. 

b.  Saturate  with  hydrogen  sulphide  (?).     Is  the  action  easily 
reversible?    Add  dilute  hydrochloric  acid  (?). 

By  what  reactions  could  you  distinguish  between  salts  of 
magnesium,  zinc,  and  cadmium? 

157.  Unknown   Substances.    Apply  to   the  instructor   for 
three    unknown    substances.     To    identify  the    anions,  follow 
the  outline  of  work  in  140.    To  identify  the  cations,  employ 


§  161]         MAGNESIUM,   ZINC,  MERCURY  119 

the  scheme  commonly  used  in  analysis  [R  660].    Present  to  the 
instructor  a  logical  and  coherent,  written  report. 

168.  Mercurous  Nitrate.    Place  about  10  g.  of  mercury  with 
15  c.c.  of  diluted  (1  : 1)  nitric  acid  in  a  small  beaker,  and  let  the 
action  go  on  for  an  hour.     Stirring  will  cause  crystallization. 
Dissolve  the  crystals  in  water  to  which  a  few  drops  of  nitric  acid 
have  been  added  (why?).     Use  this  solution  in  160. 

169.  Mercuric  Nitrate.    Boil  some  mercury  or  mercurous 
nitrate  with  excess  of  concentrated  nitric  acid.     Evaporate  the 
solution  on  a  water  bath,  moisten  with  nitric  acid,  and  dry. 

160.  Reactions  of  Salts  of  Mercury.     Use  diluted  portions  of 
mercurous  nitrate  solution  and  of  a  diluted  solution  of  any 
mercuric  salt,  and  add  to  each  the  following  reagents.     Com- 
pare the  results  in  each  case. 

a.  Litmus  paper  (?).     Explain. 

b.  Dilute  hydrochloric  acid   (?).    Treat  the  precipitate,  if 
there  is  any,  with  ammonium  hydroxide  [R  659]  (?). 

c.  Sodium  hydroxide  solution  [R  656]  (?). 

d.  Ammonium  hydroxide  [R  659]  (?). 

e.  Hydrogen  sulphide  to  saturation  [R  657]  (?). 

/.  Potassium  iodide  solution  (shake)  until  there  is  no  further 
change  (?).  What  complex  ion  is  formed?  Try  an  experiment 
to  show  that  mercuric  sulphide  gives  an  even  smaller  concen- 
tration of  mercuric-ion  than  does  this  complex  ion  (?). 

g.   Stannous  chloride  till  there  is  no  further  change  [R  655]  (?) . 

h.  A  clean  copper  nail  (?).  Determine  whether  any  copper 
goes  into  solution  (?).  Explain  (Appendix  VII). 

i.  Heat  a  little  of  a  salt  of  mercury  in  a  dry  test-tube  (?). 

/.  How  could  you  distinguish  a  solution  of  a  mercurous  and 
of  a  mercuric  salt,  respectively,  from  salts  of  silver,  copper, 
magnesium,  zinc,  and  cadmium? 

Do  magnesium,  zinc,  cadmium,  and  mercury  exhibit  the 
properties  of  typical  metallic  elements  [R  533]?  Explain. 

161.  Concentration  Cell.     Suspend  a  rod  of  tin  about  60  mm. 
long  by  a  thread  from  one  end,  and  hang  it  near  the  bottom  of 
the  graduated  cylinder.     Pour  in  through  the  dropping-funnel, 
which  must  reach  the  bottom  of  the   cylinder,   first  highly 
diluted,  dilute  hydrochloric  acid  (1  : 6  Aq.)  and  then  diluted 
(1  : 1)  stannous  chloride  solution.     Perform  the  operation  with 
care,  in  such  a  way  that  the  solutions  do  not  mix,  the  dilute 
acid  being  finally  uppermost,  and  that  the  surface  at  which 
they  meet  is  near  the  middle  of  the  rod  of  tin.     If  the  second 
solution  is  permitted  to  carry  air  bubbles  with  it,  mixing  will 
inevitably  occur.     Place  the  arrangement  where  it  will  not  be 
disturbed,  and  examine  from  time  to  time  (?).    Explain  [R  673]. 


CHAPTER  XXII. 

ALUMINIUM,  TIN,   LEAD. 

162.  Aluminium. 

a.  Record  here  the  action  of  aluminium  on  hydrochloric  acid 
(16  a)  and  its  degree  of  intensity  (?).     Try  the  action  of  the 
metal  on  dilute  sulphuric  (?)  and  dilute  nitric  acids  (?).     Com- 
pare and  explain. 

b.  Heat  some  aluminium  turnings  with  sodium  hydroxide 
solution  for  some  minutes  (?).     To  ascertain  whether  anything 
has  gone  into  solution,  neutralize  one-half  of  the  liquid  care- 
fully with  dilute  hydrochloric  acid   (?).     Test  the  precipitate 
by!63/(?). 

c.  To  the  rest  of  the  liquid  from  b  add  calcium  chloride  solu- 
tion (?).     To  what  group  of  minerals  do  compounds  allied  to 
this  belong  [R  685]  ? 

163.  Reactions  of  Aluminium  Salts.    Use  portions  of  diluted 
aluminium  sulphate  solution. 

a.  Test  the  solution  with  litmus  paper  (?).     Explain. 

b.  Add    ammonium   sulphide    solution    (?).     Filter    off   the 
precipitate,  wash  it  until  odorless  (why?),  and  ascertain  whether 
it  is  a  sulphide  or  not  (?).     Preserve  a  part  of  it  for  /. 

c.  Add  sodium  carbonate  solution  (?).     Filter  off  the  precip- 
itate, wash  it  until  free  from  sodium  carbonate   (why?),  and 
ascertain  whether  it  is  a  carbonate  or  not  (?). 

d.  Add  a  little  sodium  hydroxide  solution  (?).     Proceed  as 
in  153  e,  and  answer  the  same  questions  (?).     Explain  the  dif- 
ference in  behavior  observed  (?). 

e.  To  a  small  portion  add  sufficient  sodium  hydroxide  solu- 
tion to  redissolve  the  precipitate.    Then  add  excess  of  ammo- 
nium chloride  solution,  and  boil  (?).     Explain. 

/.   Proceed  as  in  153  g  with  a  small  part  of  the  filter  paper 
from  b  (?)  (or  use  the  method  in  153  d). 

164.  Alum.     Prepare  warm,  saturated  solutions  of  hydrated 
aluminium  sulphate  and  ammonium  sulphate  in  approximately 
equimolecular  proportions    (calculate   amounts  required),  mix 
them,  and  set  aside  (?).     Obtain  some  large  crystals  by  hanging 
a  thread  in  the  solution.     Note  the  form  and  taste   of  the 
crystals  (?). 

Dissolve  one  or  two  of  the  crystals,  and  ascertain  by  experi- 
ments selected  from  163  whether  the  solution  contains  alu- 

120 


§  168]  ALUMINIUM,   TIN,   LEAD  121 

minium-ion  (?).    Infer  whether  this  is  a  double  salt,  or  a  salt 
giving  a  complex  ion. 

165.  Mordanting. 

a.  To  some  cochineal  solution  add  any  solution  containing  a 
salt  of  aluminium  and  then  ammonium  hydroxide  (?).     Filter. 
What  becomes  of  the  coloring  matter? 

b.  Soak  a  small  piece  of  cloth  in  a  strong  solution  of  alum 
(made  in  164),  and  then  transfer  it  to  a  beaker  containing  a 
boiling  solution  of  cochineal  made  strongly  alkaline  with  ammo- 
nium  hydroxide    (?).     What   purpose   does   the   alum   serve? 
What  is  the  object  of  the  ammonium  hydroxide?    What  com- 
pounds of  aluminium  would  act  as  mordants  without  the  addi- 
tion of  a  base  (?),  and  how  do  they  so  act  [R  689]  ? 

166.  Tin.     Place  some  tin  (gran.)  in  a  test-tube  with  diluted 
nitric  acid  (1  acid:  10  Aq)  and  set  aside.     After  168,  examine 
portions   of  the   solution.     Determine  whether  it   contains  a 
salt  of  ammonium   (?),  and  explain.     Determine  whether  it 
contains  stannic-ion  or  stannous-ion  (?).     How  does  tin  behave 
with  concentrated  nitric  acid  (97  e)  ?    Explain  the  difference. 

167.  Halides  of  Tin. 

a.  Stannous  halide.     Heat  about  1  g.  of  tin  with  pure,  con- 
centrated hydrochloric  acid  (see  16  a)  (?).     Let  the  action  go 
on  until  the  acid  is  nearly  exhausted.     Use  the  solution  in  6, 
and  in  168.     Proceed  with  later  experiments  until  it  is  ready. 

b.  Stannic  halide  [Hood].     To  one-half  of  the  solution  from  a 
add  bromine-water  until  the  color  ceases  to  be  destroyed,  and 
drive   off  the   excess  of  bromine  by  warming    (?).     Use   this 
liquid  in  168. 

168.  Reactions  of  Stannous  and  Stannic  Salts.     In  a,  b,  and 
c  use  a  portion  of  each  of  the  solutions  from  167,  after  clilution, 
with  each  reagent.     Compare  the  two  results  in  each  case. 

a.  Saturate  (test?)  each  portion  with  hydrogen  sulphide  (?). 
To  part  of  each  product  add  dilute  hydrochloric  acid,  to  learn 
whether  the  action  is  easily  reversible  (?).     Filter  the  remainder 
of  each  product,  and  treat  the  precipitates,  separately,  with 
warm  yellow  ammonium  sulphide  solution  [R  697]   (?).     To 
the  resulting  liquids  add  dilute  hydrochloric  acid  (?).     Explain 
why  both  give  the  same  product  (?).     What  is  the  gas  evolved? 

b.  Add  mercuric  chloride  solution,  at  first  a  little  and  then 
in  excess,  first  to  the  stannic  (?)  and  then  to  the  stannous  solu- ' 
tion  (?).     When  the  changes  (two)  in  the  latter  are  complete, 
boil,  let  the  precipitate  settle,  filter  the  clear  part  of  the  liquid, 
and  determine  whether  the  tin  in  the  filtrate  is  now  stannous  or 
stannic  by  adding  a  drop  or  two  of  bromine-water  (see  167  b). 

c.  Add  to  each  portion  a  little  sodium  hydroxide  solution  (?). 


122  ALUMINIUM,   TIN,  LEAD  [§169 

Proceed  as  in  158  e  and  answer  the  same  questions  (?).  Ex- 
plain the  difference,  if  any,  in  behavior  observed.  What  other 
hydroxide  resembles  those  of  tin  and  zinc? 

d.  Boil  a  small  portion  of  the  stannic  solution  with  tin  (gran.) 
for  several  minutes.  Now  add  mercuric  chloride  solution  (?) 
and  compare  with  the  results  in  b  (?).  Account  for  the  change 
in  the  stannic-ion  (?).  What  kind  of  chemical  change  was  this  ? 

169.  Apply  to  the  instructor  for  two  unknown  substances. 
Identify  them,  and  report  the  result,  as  directed  in  140  and  157. 

170.  Lead. 

a.  Dissolve  1  g.  of  lead  acetate  in  20  c.c.  of  water,  place  in 
it  several  pieces  of  granulated  zinc,  and  set  aside  for  an  hour  or 
two.     After  171  devise  a  way  of  precipitating  any  remaining 
lead-ion  and  showing  the  presence  of  zinc-ion  in  the  solution. 

b.  Wash  some  of  the  lead  from  a  with  distilled  water,  and  see 
whether  it  is  possible  to  get  washings  which  show  no  reaction 
with  hydrogen  sulphide  (?).     Account  for  what  you  observe. 

171.  Reactions  of  Lead  Salts.     Use  diluted  lead  nitrate. 
a.  Test  with  litmus  paper  (?). 

6.  Saturate  (test?)  with  hvdrogen  sulphide  (?).  Is  the 
action  easily  reversed? 

c.  Add  dilute  hydrochloric  acid  (?).     Filter,  dilute  the  fil- 
trate with  5-10  volumes  of  water,  and  saturate  with  hydrogen 
sulphide  (?).     Explain.     What  other  chlorides  are  "insoluble"? 

d.  Add  sodium  hydroxide  (?),  first  a  little,  then  in  excess. 
What  other  hydroxides  resemble  this  one? 

e.  Add    potassium    iodide    solution    (?).     Boil,   filter,   and 
examine  the  filtrate  (?).     Infer  a  property  of  lead  iodide  (?). 

/.   Potassium  dichromate  solution  (?).    Proceed  as  in  150  g  (?). 
g.  Dilute  sulphuric  acid  (?).     What  sulphates  are  insoluble? 

172.  Lead  Dioxide. 

a.  Warm  and  agitate  1  g.  of  minium  with  5-6  c.c.  of  dilute 
nitric  acid  until  it  no  longer  changes  in  color  (?).     Dilute  with 
water,  and  filter.     Reserve  the  precipitate  for  b  and  c.     Show 
by  tests  selected  from  171  that  lead-ion  is   present  in  the  fil- 
trate.    What  theory  of  the  nature  of  red  lead  is  suggested  by 
this  action  [R  701]  ? 

b.  Treat  a  part  of  the  precipitate  from  a  with  sodium  hy- 
droxide solution   (?).     Record  here  the  action  of  hydrochloric 
acid  upon  lead  dioxide  (29  d)  and  explain  it  (?). 

c.  Allow  the  rest  of  the  precipitate  from  a  to  dry,  place  it 
in  an  evaporating-dish,  and  direct  upon  it  a  stream  of  hydrogen 
sulphide  (?).     Explain. 

173.  Do  aluminium,  tin,  and  lead  exhibit  the  properties  of 
typical  metallic  elements  [R  533]  ?    Explain. 


CHAPTER  XXIII. 

ARSENIC,    ANTIMONY,    BISMUTH. 

174.  Arsenic. 

a.  Heat  one  particle  of  arsenic  in  a  hard  glass  test-tube  (?). 

b.  Roast  a  particle  of  arsenic  on  a  crucible  lid  (?).    Note  the 
behavior  and  odor  (?). 

c.  Mix  a  pinch  of  pulverized  arsenic  trioxide  with  wood 
charcoal  (pulv.).    Heat  the  mixture  strongly  in  a  dry  test- 
tube  (?).     Compare  result  with  a  (?). 

d.  Boil  0.5  g.  of  arsenic  (pulv.)  with  excess  of  nitric  acid  (?) . 
Compare  with  105  b.     Use  the  solution  for  177  e. 

175.  Arsenic  Trioxide  and  Arsenious  Chloride. 

a.  Boil  0.5  g.  of  arsenic  trioxide  with  water  (?).    Test  the 
solution  with  litmus  (?).    Now  add  sodium  hydroxide  solution, 
and  boil  (?).    To  what  class  of  oxides  does  the  trioxide  appear 
to  belong?    Formulate  the  whole  change. 

b.  Boil  1  g.  of  the  trioxide  with  2-3  c.c.  of  concentrated 
hydrochloric  acid  (?).     To  what  class  of  oxides  does  it  appear 
now  to  belong?    Formulate  this  change.     Set  aside  and  ex- 
amine later  (?).     What  are  the  crystals  [R  710]  ?    Is  this  action 
reversible?    Use  the  solution  for  c  and  178. 

Is  arsenic  a  typical  metallic  element?    Is  it  a  metal  at  all? 
Give  reasons  taken  from  a  and  b. 

c.  Take  a  small  part  of  the  solution  from  b  (setting  aside 
the  rest),  dilute  with  water,  and  saturate  with  hydrogen  sul- 
phide (?).     Divide  into  two  parts.     With  one,  try  whether  the 
action  is  easily  reversible  (?).     Filter  the  other  and  heat  the 
precipitate  with  yellow  ammonium  sulphide  solution  (?).     What 
other  sulphide  behaved  in  this  way?     Now  add  dilute  hydro- 
chloric acid  to  the  liquid   (?).     Explain.     What  is  the  gas 
evolved? 

176.  Arsenites.    Use  portions  of  diluted  potassium  arsenite 
solution. 

a.  Add   silver   nitrate    solution   (?),  then   ammonium   hy- 
droxide (?). 

b.  Add  cupric  sulphate  solution  [R  712]  (?). 

c.  Test  the  solution  with  litmus  (?).     What  substances  must 
be  present?    Saturate  with  hydrogen  sulphide  (?). 

177.  Arsenic  Acid  and  Arsenates.     For  a,  b,  c,  and  d,  use 
portions  of  diluted  potassium  arsenate  solution. 

123 


124  ARSENIC,  ANTIMONY,   BISMUTH      [§  178 

a.  Add  silver  nitrate  solution   (?).    Add  now  ammonium 
hydroxide  (?). 

b.  Add  magnesia  mixture  (106  c)   (?).     Compare  with  152 
b  (?). 

c.  Add  to  ammonium  molybdate  solution  as  in  106  c  (?). 

d.  Add  2-3  drops  of  dilute  hydrochloric  acid  (?)  and  saturate 
with  hydrogen  sulphide  (?).     Now  add  excess  of  concentrated 
hydrochloric  acid  and  saturate  again  (?),  heating  to  assist  the 
action.     Explain. 

e.  Neutralize    the    solution   from    174   d   with   ammonium 
hydroxide,  avoiding  excess,  and  use  tests  selected  from  a,  b, 
and  c  (?). 

178.  Arsine    [HooD.     CARE!    POISON].      Arrange    a    side- 
neck  test-tube  (or  small  flask)  with  safety  and  straight  delivery 
tubes  and  nozzle  to  generate  and  burn  hydrogen.     Place  in  it 
a  piece  of  chemically  pure  zinc,  and  add  pure  hydrochloric  acid 
[Side-shelf].    When  the  air  has  been  displaced  (CARE.    Test?), 
light  the  gas  and  hold  a  crucible  lid  in  the  flame  (?).     If  there 
is  no  deposit,  add  a  drop  or  so  of  the  solution  of  arsenic  tri- 
chloride  (176  b},  observe  the  appearance  of  the  flame,  and 
obtain  a  deposit  on  the  crucible  lid  (?).     What  kind  of  chemical 
change  takes  place  in  the  flame  (see  72  6)?    Heat  the  tube, 
through  which  the  gas  passes  to  the  nozzle,  with  a  Bunsen 
flame   (?  Marsh's  test).    When  these  experiments  are  com- 
pleted, fill  the  test-tube  with  water  to  stop  the  action. 

Apply  bleaching  powder  solution  (fresh)  to  the  deposit  (?). 

Can  arsine  be  made  according  to  the  general  method  con- 
sidered in  116?  What  other  hydrides  behave  like  arsine  when 
heated? 

179.  Antimony. 

a,  b.     Proceed  as  in  174  a  and  b,  using  antimony  (?). 

180.  Antimony  Trioxide. 

a.  To  obtain  the  trioxide,  heat  2-3  g.  of  pulverized  antimony 
with  concentrated  nitric  acid  in  a  small  flask  [Hood]  (?).     How 
should  you  determine  whether  the  product  was  a  nitrate  or 
not?  (?).     What  other  metal  behaved  similarly  when  treated 
with  nitric  acid?    Compare  with  arsenic  (174  d  and  177  e)  (?). 
Dilute,  filter,  wash  well  [Note  38,  p.  85],  and  use  in  6,  c,  d,  and  e. 

b.  Boil  a  small  part  with  water  (?).     Add  sodium  hydroxide 
solution,  and  boil  (?).    What  kind  of  oxide  is  it? 

c.  Boil  a  small  part  with  hydrochloric  acid  (?),    What  kind 
of  oxide  is  it? 

d.  Boil  a  part  with  an  equal  amount  of  potassium-hydrogen 
tartrate  in  5-6  c.c.  of  water  (?).     Filter,  and  set  the  filtrate 
aside  (?).     What  are  the  crystals? 


§186]       ARSENIC,  ANTIMONY,   BISMUTH          125 

e.  Boil  the  rest  persistently  with  2-3  c.c.  of  concentrated 
nitric  acid  (?).  Evaporate  [Hood]  the  clear  liquid,  and  heat 
the  residue  a  little  below  a  red  heat  [R  715]  (?). 

181.  Antimony  Trichloride  and  Trisulphide. 

a.  Treat  about  0.5  g.  of  antimony  trichloride  with  water  (?), 
and  test  the  liquid  with  litmus  paper  (?).  Add  more  water, 
warm,  and  ascertain  whether  the  action  is  reversible  by  adding 
drop  by  drop  (shake  between  drops)  concentrated  hydrochloric 
acid  (?).  When  the  liquid  has  become  clear  add  a  large  amount 
of  water  (?).  What  law  is  illustrated?  Finally,  add  concen- 
trated hydrochloric  acid  again  (?),  and  use  the  solution  in  6. 

How  does  this  action  differ  from  that  of  water  upon  phos- 
phorus trichloride  (107  6)  and  upon  arsenic  trichloride  [R  710]? 
What  is  the  significance  of  this  difference? 

6.  Dilute  the  liquid  from  o,  saturate  with  hydrogen  sulphide 
(?),  and  proceed  as  in  175  c  (?).  Answer  the  same  questions. 

182.  Stibine.     Repeat  178,  using  antimony  trichloride  (?). 

183.  Bismuth.     Prepare  a  match  (or  splinter  of  wood)  as  in 
86,  and  proceed  as  in  145  /,  using  any  bismuth  salt  (?).     What 
metals  are  obtainable  in  this  precise  way?     Could  zinc,  mercury, 
silver,  and  aluminium  be  so  obtained?    Explain. 

184.  Compounds  of  Bismuth. 

a.  Warm  about  1  g.  of  bismuth  with  8-10  c.c.  of  diluted 
(1  : 1)  nitric  acid  (?).  Concentrate  to  3  c.c.  and  set  aside 
[R  718]  (?).  Compare  this  result  with  arsenic  (174  d)  and 
antimony  (180  a),  and  interpret  (?). 

6.  Proceed  as  in  181  a  (first  par.),  using  bismuth  nitrate  (or 
the  product  from  a)  and  nitric  acid,  instead  of  the  salt  and 
acid  there  employed  (?). 

c.  Take  1-2  c.c.  of  bismuth  nitrate  solution,  dilute  it,  and 
clear  up  with  nitric  acid  if  necessary.     Saturate  a  part  with 
hydrogen  sulphide  (?),  and  proceed  as  in  175  c  (?).     Compare 
with  the  sulphides  of  arsenic  and  antimony  (?). 

d.  To  the  remainder  of  the  solution  of  bismuth  nitrate  add 
sodium  hydroxide  (?),  at  first  a  little,  and  then  in  excess  (?). 
Compare  this  hydroxide  with  the  oxides  of  arsenic  (175  a)  (?) 
and  of  antimony  (180  6)  (?). 

Filter  off  the  precipitate,  ignite  it  in  a  porcelain  crucible, 
and  note  the  color  (?)  when  hot  (?)  and  when  cold  (?). 

185.  Do  arsenic,  antimony,  and  bismuth  exhibit  the  prop- 
erties of  typical  metallic  elements?    If  not,  in  what  respects  do 
they  fail  to  do  so? 

186.  Apply  to  the  instructor  for  two  unknown  substances. 
Identify  them,  and  report  the  result,  as  directed  in  140  and  157. 
Do  not  use  Marsh's  test  for  arsenic. 


CHAPTER  XXIV. 

CHROMIUM,  MANGANESE. 

187.  Chromates.     Melt  5  g.  of  potassium  carbonate  with 
equal  amounts  of  potassium  hydroxide   (omit  this  from  the 
equation)  and  potassium  nitrate  (include  only  oxygen,  from  this, 
in  the    quation)  at  a  low  temperature  in  an  iron  :rucible  [Store- 
room] and  stir  in  (use  the  reverse  end  of  a  file)  5  g.  of  powdered 
chromitc.     Heat  strongly  [Blast-lamp]  for  several  minutes  (?). 
When  the  mass  has  cooled  dissolve  it  in  a  little  boiling  water. 
Filter,  and  add  dilute  nitric  acid  to  the  solution  until  it  is  acid  (?). 
Note  the  change  in  color  (?). 

188.  Bichromates    and   Chromates.    Take  some  potassium 
dichromate  solution  and  run  into  it  potassium  hydroxide  solu- 
tion from  a  burette  till  the  change  in  color  is  complete.     A 
test-tube  trial  will  show  the  tint  to  be  reached.     Concentrate 
the  solution  and  allow  it  to  crystallize  (?).     What  kind  of  salt 
(neutral,  acid,  basic,  double,  or  complex)  is  potassium  dichro- 
mate essentially?     What  are  the  colors  of  dichromate-ion  and 
of  chromate-ion? 

189.  Chromic  Anhydride.     Make  a  cold  saturated  solution  of 
5  g.  of  sodium  dichromate,  add  to  it  two  volumes  of  concen- 
trated sulphuric  acid  in  a  beaker,  and  cool  (?).     Filter  through 
a  small  plug  of  asbestos,  and  dry  the  precipitate  by  smearing 
it  on  a  piece  of  broken  bisque  plate  [Storeroom]. 

190.  Chromic   Oxide.      Pulverize  potassium  dichromate  (10 
g.)  thoroughly  with  one-fifth  its  weight  of  sulphur,  and  heat 
with  the  blast-lamp  in  a  porcelain  crucible  for  fifteen  minutes. 
Grind  up  the  resulting  mass  in  a  mortar  with  water,  filter, 
wash  the  green  residue  (?),  and  dry  it  on  a  radiator  for  use 
in  191. 

Make  a  borax  bead,  dissolve  a  particle  of  chromic  oxide  in 
it,  and  note  the  effects  of  the  oxidizing  and  reducing  flames 
upon  it  0).  All  chromium  compounds  give  the  same  result.  If 
chromic  sulphate  had  been  used,  what  would  have  been  the 
nature  of  the  chemical  action? 

101.  Chromic  Chloride.  Mix  the  chromic  oxide  prepared  in 
190,  with  one-third  its  weight  of  pulverized  wood  charcoal, 
make  into  a  stiff  paste  with  some  starch,  and  mold  the  mixture 
into  little  pellets  of  the  size  of  peas.  Coyer  these  completely 
with  a  layer  of  charcoal  powder  (why?)  in  a  closed  crucible. 

126 


§  195]  CHROMIUM,   MANGANESE  127 

dry  them  by  heating  gently  with  the  Bunsen  flame,  and  let  them 
cool  before  exposing  them  to  the  air  (why?).  Place  them  in  a 
piece  of  hard  glass  tubing.  Then  connect  with  a  chlorine 
apparatus,  and,  when  the  chlorine  gas  has  reached  the  pellets 
and  completely  displaced  the  air  (why?),  heat  strongly  with  a 
blast-lamp.  Conduct  any  superfluous  chlorine  into  a  test- 
tube  filled  with  sodium  hydroxide.  Describe  the  substance 
which  is  formed,  and  try  its  solubility  in  water  and  acids. 

192.  Chrome-Alum.     Dissolve  10  g.  potassium  dichromate  in 
water,  add  the  amount  (calculated)  of  sulphuric  acid  necessary 
to  form  potassium  sulphate  and  chromium  sulphate,  warm  and 
add  alcohol  (7-10  c.c.),  a  little  at  a  time,  until  the  yellow  color 
has  entirely  given  place  to  a  pure,  bright  green.     The  action 
takes  some  time  to  reach  completion.     Note  the  odor  (?).     Set 
the  greater  part  of  the  solution  aside  to  evaporate  spontane- 
ously.    Concentrate  the  smaller  portion  on  the  water  bath  until 
crystals  appear.     Examine  the  form  and  color  of  the  crystals 
from  both  portions  (?).     What  is  the  color  of  their  solution  in 
water?     What  is  the  color  of  chromic-ion? 

193.  Reactions  of  Chromic  Salts.     Make  a  solution  of  chrome- 
alum.     What  are  the  ions  in  the  solution? 

a.   Boil  a  portion  for  some  time  [R  730]. 
6.  To  another  portion   add  sodium  hydroxide  solution,  at 
first  a  little  (?),  then  in  excess  (?).     Boil  [R  729]. 

c.  Add  ammonium  sulphide   (?).     Filter  off  the  precipitate, 
wash  it  until  odorless,  and  determine  whether  it  is  a  sulphide. 

d.  Add  excess  of  sodium  hydroxide  solution  and  then  a  large 
volume  of  bromine-water,  and  heat  (?).     Try  another  portion, 
using  lead  dioxide  instead  of  bromine  (?).     Infer  the  nature  of 
the  action  from  the  change  in  color. 

194.  Reactions  of  Chromates.     For  a,  6,  c,  d,  use  diluted  po- 
tassium chromate  solution.     What  are  the  ions  in  the  solution? 

a.  Acidify  a  part  of  the  solution  with  dilute  sulphuric  acid  (?). 
Concentrate  and  set  aside  to  crystallize  (?). 

6.  Recall  the  actions  of  hydrogen  sulphide,  of  sulphurous 
acid,  and  of  hydrogen  peroxide,  on  such  an  acid  solution  (?). 

c.  Add  ammonium  sulphide,  heat  and  maintain  at  the  boil- 
ing-point, noting  two  distinct  changes  (?),  then  acidify  (?). 

d.  Add  lead  nitrate  and  barium  chloride  solutions  to  sepa- 
rate portions  (?). 

e.  Repeat  d  with  potassium  dichromate  solution  (?).     Com- 
pare the  results  and  explain. 

195.  Manganates  and  Permanganates. 

a.  Fuse  a  mixture  of  5  g.  of  potassium  hydroxide,  2.5  g.  po- 
tassium chlorate  (include  only  the  oxygen,  from  this,  in  the  equa- 


128  CHROMIUM,   MANGANESE  [§  196 

tion),  and  5  g.  finely  powdered  manganese  dioxide,  at  a  red 
heat,  in  an  iron  crucible  [Storeroom],  stirring  with  the  reverse 
end  of  a  file,  until  effervescence  ceases  (?).  Add  the  last  ingre- 
dient gradually.  Treat  the  mass  with  a  small  amount  of  cold 
water,  decant  the  clear  liquid  away  from  the  precipitate,  and 
use  it  in  b,  c,  and  d.  What  is  the  color  of  manganate-ion? 

6.  Dilute  a  part  of  the  clear  green  solution  with  a  very  large 
amount  of  water  in  a  beaker  (?).  If  no  change  should  occur, 
pass  carbon  dioxide  into  the  diluted  solution  (?).  What  is  the 
color  of  permanganate-ion?  How  does  this  substance  differ 
from  manganate-ion? 

c.  Add  a  few  drops  of  alcohol,  and  warm  (?). 

d.  To  the  rest  add  a  boiling  solution  of  oxalic  acid  (?). 

e.  Repeat  c  and  d  with  potassium  permanganate  solution, 
acidified  by  adding  two  or  three  times  its  volume  of  dilute  sul- 
phuric acid  (?). 

/.  Recall  the  actions  of  hydrogen  peroxide  (60  c),  hydrogen 
sulphide  (73  /),  and  sulphurous  acid  (83  g)  on  acidified  potas- 
sium permanganate  solution  (?). 

196.  Reactions  of  Manganous  Salts.      Use   any  manganous 
salt.     What  is  the  color  of  manganous-ion? 

a.  Borax  bead  in  the  oxidizing  (?)  and  reducing  (?)  flames. 

b.  Bead  of  a  mixture  of  sodium  carbonate  and  sodium  nitrate 
on  a  platinum  wire  with  any  manganese  compound  (?). 

c.  To  a  diluted  solution  of  a  manganous  salt,  add  ammo- 
nium sulphide  (?).     Is  the  product  a  sulphide? 

d.  To  another  portion  add  sodium  hydroxide   (?).     Divide 
into  two  parts.     Shake  one  with  air  (?).    To  the   other  add 
bromine-water,  and  warm  (?). 

197.  Apply  to  the  instructor  for  two  unknown  substances. 
Identify  them,  and  report  the  result,  as  directed  in  140  and  167. 


CHAPTER  XXV. 

IRON,  COBALT,  NICKEL. 

198.  Iron.    Recall  the  preparation  of  iron  from  an  oxide 
(20),  and  the  action  of  the  metal  on  dilute  acids  (16  a)  (?). 

199.  Reactions  of  Ferrous  and  Ferric  Salts :  I. 

a.  Borax  bead  with  any  compound  of  iron  (use  the  oxide)  in 
the  reducing  (?)  and  oxidizing  (?)  flames. 

6.  Recall  the  action  of  heat  upon  ferric  nitrate  (36  a)  and 
upon  ferric  sulphate  (82)  (?). 

Prepare  a  dilute  solution  of  ferrous-ammonium  sulphate  [Note 
37,  p.  68].  Dilute  some  ferric  chloride  solution  [Note  40,  p. 
108].  Use  portions  of  these  solutions,  and  add  to  each  the 
following  reagents.  Compare  the  results  in  each  case. 

c.  Ammonium  hydroxide  (?).     Shake  with  air  (?). 

d.  Potassium  ferrocyanide  solution  (?). 

e.  Potassium  ferricyanide  solution  (?)  and  add  much  water. 
/.    Ammonium  thiocyanate  solution  (?). 

g.  Ascertain  by  tests  whether  the  commercial  hydrochloric 
acid  contains  ferrous-ion  or  ferric-ion  (?).  Show  that  it  con- 
tains also  sulphuric  acid  (?). 

200.  Reactions  of  Ferrous  and  Ferric  Salts:  II.  Reductions 
and  Oxidations.    Use  diluted  ferrous-ammonium  sulphate  and 
diluted  ferric  chloride  solutions. 

a.  To  portions  of  each  solution  add  ammonium  sulphide 
solution  (?).  Ascertain  in  each  case  whether  the  action  is 
easily  reversible  (?).  Explain  the  behavior  of  the  ferric  chlor- 
ide solution  [R  756]  (?).  How  could  you  determine  whether 
the  free  sulphur  was  formed  before  or  after  the  acidification  ? 

6.  To  portions  of  each  solution  add  potassium  iodide  solu- 
tion (?).  To  a  little  starch  emulsion  add  a  few  drops  of  the 
ferric-potassium-iodide  mixture  (?). 

c.  Saturate  (test?)  a  portion  of  the  ferrous  solution  with 
hydrogen  sulphide  (?).    Explain  in  terms  of  the  ion-product 
constant    (?).    Now   add   ammonium   hydroxide    (?).     Filter. 
Wash  the  precipitate  until  odorless,  and  determine  whether  it 
is  a  sulphide  or  hydroxide  (?).     Explain  in  terms  of  the  ion- 
product  constant. 

d.  Saturate  (test?)  a  portion  of  the  ferric  solution  with  hy- 
drogen sulphide  (?).    Filter.    What  is  the  precipitate  (test?)? 
Examine  the  clear  filtrate,  and  determine,  by  means  of  tests 

129 


130  IRON,  COBALT,  NICKEL  [§201 

from  199  d,  e,  and  /,  whether  ferric-ion  or  ferrous-ion  is  pres- 
ent (?).  Formulate  the  action  of  the  hydrogen  sulphide. 

e.  Boil  a  portion  of  the  ferric  solution  with  excess  of  pul- 
verized iron  for  several  minutes.  Filter,  and  apply  to  part  of 
the  clear  filtrate  (color?)  tests  selected  from  199  d,  e,  and  /  (?). 
Formulate  the  action  of  the  iron.  Use  the  rest  of  the  filtrate 
in/. 

/.  To  2  c.c.  of  potassium  permanganate  solution  add  a  large 
excess  of  dilute  sulphuric  acid  (?).  Add  this  mixture  drop  by 
drop  to  the  rest  of  the  filtrate  from  e  until  the  pink  color  is 
permanent  [R  744]  (?).  Apply  to  this  liquid  tests  from  199  d, 
e,  and  /  (?).  Formulate  the  action  in  terms  of  ions  alone. 
Which  kinds  of  ionic  chemical  change  have  been  illustrated 
here?  How  could  this  action  be  used  for  estimating  iron? 

What  other  oxidizing  agents  convert  ferrous  into  ferric  salts 
(see94/)? 

201.  Hydrolysis.     Dissolve  0.5  g.  each  of  ferric  sulphate  and 
ferrous-ammonium  sulphate  separately  in  water,  and  warm 
very  slightly.     Observe  the  tints  by  looking  downward  through 
the  solutions  at  a  piece  of  white  paper  (?).    Test  each  solution 
with  Congo  red  paper,  compare  (?),  and  interpret  the  results. 
Now  add  some  pure  sulphuric  acid  to  each  and  observe  the 
tints  again.     Explain.    What  are  the  colors  of  ferrous-ion  and 
ferric-ion,  respectively?    Which  of  these  allotropic  forms  of 
the  element  is  more  typically  metallic? 

202.  Iron- Ammonium  Alum. 

a.  Weigh  6  g.  of  ferric  sulphate  into  an  evaporating-dish. 
Weigh  out  an  equimolecular  quantity  (calculate)  of  ammo- 
nium sulphate.  Dissolve  the  salts  separately,  each  in  the  mini- 
mum amount  of  boiling  water,  mix  the  solutions,  and  set 
aside  (?).  Describe  the  crystals  (?).  Collect  them  upon  a 
filter,  wash  them  free  from  the  mother-liquor,  and  dry  with 
filter  paper. 

6.  Ascertain  (see  199  c,  d,  e)  whether  iron-alum  is  a  double 
salt,  or  a  salt  of  a  complex  acid  (?). 

203.  Ferrocyanides  and  Ferricyanides.    Use  diluted  potas- 
sium ferrocyanide  solution. 

a.   Add  ammonium  hydroxide  (?)  and  compare  with  199  c  (?). 
6.   Add    ammonium   sulphide    solution   and    compare   with 
200  a  (?).     Is  ferrous-ion  present? 

c.  Add  bromine-water   (shake)  in  excess,  and  boil  off  the 
superfluous  bromine.    To  a  part  of  the  liquid  add  ferric  chloride 
solution  (see  199  d  and  e)  (?). 

d.  To  the  rest  of  the  liquid  from  c  apply  the  tests  in  199  c 
and  /  (?).    Is  ferric-ion  present? 


§206]  IRON,   COBALT,   NICKEL  131 

204.  Reactions  of  Cobalt  Salts.    For  b  and  c  use  diluted 
cobalt  chloride  solution. 

a.  Borax  bead  in  oxidizing  (?)  and  reducing  (?)  flames. 
6.   Sodium  hydroxide  solution,  first  a  little  (?),  then  in  excess, 
and  warm  (?). 

c.  Ammonium  sulphide  solution  (?). 

205.  Reactions  of  Nickel  Salts.     For  b  and  c  use  diluted 
nickel  sulphate  solution. 

a,  6,  c.     Same  as  in  204. 

206.  Apply  to  the  instructor  for  two  unknown  substances. 
Identify  them,  and  report  the  result,  as  directed  in  140  and 
157. 


APPENDIX. 
I.     Correction  of  Barometric  Readings. 

To  reduce  the  reading  taken  at  room  temperature  (Temp.) 
to  the  corresponding  height  of  a  column  of  mercury  at  0°,  sub- 
tract the  proper  number  in  the  second  column  (Corr'n)  from 
the  actual  reading  in  millimeters.  [See  Note  31,  p.  18.] 


Temp. 

Corr'n. 

Temp. 

Corr'n. 

Temp. 

Corr'n. 

12 

1.6 

17 

2.2 

23 

3.0 

13 

1.7 

18.5 

2.4 

24.5 

3.2 

14 

1.8 

20 

2.6 

25 

3.3 

15 

2.0 

21.5 

2.8 

26 

3.4 

II.     Tension  of  Aqueous  Vapor  in  Millimeters. 


Temp. 

Press. 

Temp. 

Press. 

Temp. 

Press. 

0° 

4.6 

16° 

13.5 

26° 

25.1 

5 

6.5 

17 

14.4 

27 

26.5 

8 

8.0 

18 

15.4 

28 

28.1 

9 

8.6 

19 

16.3 

29 

29.8 

10 

9.2 

20 

17.4 

30 

31.5 

11 

9.8 

21 

18.5 

31 

33.4 

12 

10.5 

22 

19.7 

32 

35.4 

13 

11.2 

23 

20.9 

33 

37.4 

14 

11.9 

24 

22.2 

34 

39.6 

15 

12.7 

25 

23.6 

100 

760.0 

Aluminium 
Copper 


in.     Specific  Heats  of  Metals. 


0.214 
0.095 


Iron 
Lead 


0.114 
0.031 


Magnesium 
Zinc 


0.250 
0.095 


APPENDIX  133 

IV.  Solubilities  of  Bases  and  Salts  in  Water  at  18°. 


K 

Na 

Li 

Ag 

Tl 

Ba 

Sr 

Ca 

Mg 

Zn 

Pb 

Cl 

32.95 
3.9 

35.86 
5.42 

77.79 
13.3 

o.o3i6 

0.0410 

0.3 
0.013 

37.24 
1.7 

51.09 
3.0 

73.19 
5.4 

55.81 
5.1 

203.9 
9.2 

1.49 
0.05 

Br 

/y-    Qt* 
OO.OU 

4.6 

88.76 
6.9 

168.7 
12.6 

0.041 
0.066 

0.04 
0.0215 

103.6 
2.9 

96.52 
3.4 

143.3 
5.2 

103.1 
4.6 

478.2 
9.8 

0.598 
0.02 

I 

137.5 
6.0 

177*9 
84 

161.5 
8.5 

0.0635 
0.071 

0.006 
0.0317 

201.4 
3.8 

169.2 
3.9 

200 

4.8 

148.2 
4.1 

419 
6.9 

0.08 
0.0,2 

F 

92.56 
12.4 

4.44 
1.06 

0.27 
0.11 

195.4 
13.5 

72.05 
3 

0.16 
0.0j92 

0.012 
0.001 

0.0016 
0.032 

0.0076 
0.0214 

0.005 
0.035 

0.07 
0.003 

NO, 

30.34 
2.6 

83.97 
7.4 

71.43 
7.3 

213.4 
8.4 

8.91 
0.35 

8.74 
0.33 

66.27 
2.7 

121.8 
5.2 

74.31 
4.0 

117.8 

4.7 

51.66 
1.4 

cios 

6.6 
0.52 

97.16 
6.4 

313.4 
15.3 

12.25 
0.6 

3.69 
0.13 

35.42 
1.1 

174.9 
4.6 

179.3 
5.3 

126.4 
4.7 

183.9 
5.3 

150.6 
3.16 

BrO8 

6.38 
0.38 

36.67 
2.2 

152.5 
8.20 

0.59 
0.025 

0.30 
0.009 

0.8 
0.02 

30.0 
0.9 

85.17 
2.3 

42.86 
1.5 

58.43 
1.8 

1.3 
0.03 

I03 

7.62 
0.35 

8.33 
0.4 

80.43 
3.84 

0.004 
0.0314 

0.059 
0.0216 

0.05 
0.001 

0.25 
0.0257 

0.25 
0.007 

6.87 
0.26 

0.83 
0.02 

0.002 
0.043 

OH 

142.9 
18 

116.4 
21. 

12.04 
5.0 

0.01 
0.001 

40.04 
1.76 

3.7 
0.22 

0.77 
0.063 

0.17 
0.02 

0.001 
0.032 

0.0,5 
0.045 

0.01 

0.034 

804 

11.11 
0.62 

16.83 
1.15 

35.64 
2.8 

0.55 
0.020 

4.74 
0.09 

0.0323 
0.0410 

0.011 
0.036 

0.20 
0.015 

35.43 

2.8 

53.12 
3.1 

0.0041 
0.0313 

Cr04 

63.1 
2.7 

61.21 
3.30 

111.6 
6.5 

0.0025 
0.0315 

0.006 
0.031 

0.0338 
0.0415 

0.12 
0.006 

0.4 
0.03 

73.0 
4.3 

.   .   . 

0.042 
0.0«j5 

Ca04 

30.27 
1.6 

3.34 
0.24 

7.22 
0.69 

0.0035 
0.032 

1.48 
0.030 

0.0086 
0.0S38 

0.0046 
0.0326 

0.0,56 
0.0443 

0.03 
0.0027 

0.036 
0.044 

0.0315 
0.065 

C03 

108.0 
5.9 

19.39 
1.8 

1.3 
0.17 

0.003 
0.031 

4.95 
0.10 

0.0023 
0.0311 

0.0011 
0.047 

0.0013 
0.0313 

0.1 
0.01 

0.004? 
0.0,3? 

o.osi 

0.043 

The  upper  number  in  each  square  gives  the  number  of  grams  of  the 
anhydrous  salt  held  in  solution  by  100  c.c.  of  water.  The  lower  number  is 
the  molar  solubility,  i.e.,  the  number  of  moles  contained  in  one  liter  of  the 
saturated  solution.  * 


134 


APPENDIX 


40°  -          50e 

Temperature 


70°          89°         90°         100 


APPENDIX 


135 


VI.    Degree  of  lonization  of  lonogens. 

Except  where  otherwise  specified,  the  figures  give  the  fraction 
ionized  in  a  normal,  aqueous  solution  (usually  at  18°).  Sub- 
traction of  the  figures  from  the  unity  gives  the  extent  to  which 
the  ions  will  unite  when  brought  together  in  normal  concen- 
tration. At  greater  dilutions  the  ionization  is  greater  and  the 
union  of  ions  less. 

ACIDS. 


HN03 

0.82 

H.H2P04  (N/2) 

0.17 

HNO3  (cone.) 

0.09 

H.HC2O4  (N/10) 

0.50 

HC1 

0.78 

H.HC4H406  (N/10 

)     0.08 

HC1  (cone.) 

0.13 

H.C2H302 

0.024 

HC1  (N/2) 

0.85 

H.C2H302  (N/10) 

0.013 

H2SO4 

0.51 

H.HC03  (N/10) 

0.0217 

H2SO4  (cone.) 

0.027 

H.HC03  (N/25) 

0.0221 

HBr  (N/2) 

0.90 

H.HS  (N/10) 

0.037 

HI  (N/2) 

0.90 

H.H2BO3  (N/10) 

0.031 

HC103  (N/2) 
HMnO4  (N/2) 

0.88 
0.93 

HNC  (N/10) 

0.0,1 

BASES. 

KOH 

0.77 

Sr(OH)a  (N/64) 

0.93 

NaOH 
Ba(OH)2 

0.73 

0.69 

Ba(OH)2  (N/64) 
AgOH  (N/1783) 

0.92 
0.39 

NH4OH 

0.024 

HOH 

0.0.1 

Ca(OH)2  (N/64) 

0.90 

SALTS. 

KC1 

0.75 

Na2CO3 

0.40 

KBr  (N/32) 

0.92 

Na.HC03 

0.52 

KC103  (N/2) 

0.79 

Na,.HP04  (N/32) 

0.83 

KN03 

0.64 

NaC2H302 

0.53 

K2S04 

0.53 

Na2C4H4O6  (N/32) 

0.78 

K2C03 

0.49 

BaCl2 

0.57 

KMnO4  (N/32) 

0.92 

CaS04  (N/100) 

0.63 

K2Cr2O7  (N/32) 

0.94 

CuSO4 

0.22 

NH4C1 

0.74 

AgN03 

0.58 

NaCl 

0.67 

CdS04 

0.22 

Na2S04 

0.44 

ZnSO4 

0.24 

Na2SO8  (N/32) 

0.82 

HgCl, 

(<0.01) 

136  APPENDIX 

VII.     Electromotive  Series. 

The  electromotive  force  of  a  cell,  in  which  each  of  the  fol- 
lowing metals  constitutes  in  turn  the  negative  pole  (and  gold, 
e.g.,  the  positive),  diminishes  in  the  order  given.  The  tendency 
to  enter  the  ionic  condition  in  a  solution  already  containing 
the  same  ion  in  normal  concentration  diminishes  in  the  same 
order,  and  hence  the  ionic  form  of  each  of  these  metals  (in 
normal  concentration)  is  discharged  and  the  metal  liberated 
by  every  metal  preceding  it  in  the  series. 

Potassium  Cadmiurn  Arsenic 

Sodium  Iron  (Fe**)  Bismuth 

Barium  Thallium  Antimony 

Strontium  Cobalt  Mercury  (Hg**) 

Calcium  Nickel  Silver 

Magnesium  Tin  (Sn")  Palladium 

Aluminium  Lead  Platinum 

Manganese  Hydrogen  Gold 

Zinc  Copper  (Cu") 


M88208 


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REFERENCES 

TO   THE 

GENERAL  CHEMISTRY  FOR  COLLEGES 


The  references  given  in  this  Laboratory  Outline  are  to  the  In- 
troduction to  General  Inorganic  Chemistry.  These  references  are 
arranged  below  in  numerical  order,  and  opposite  to  them  are  placed 
the  corresponding  pages  in  the  General  Chemistry  for  Colleges. 


Inorganic 

College 

Inorganic. 

College 

Inorganic 

College 

Inorganic 

College 

46 

31 

260 

387 

263 

600 

398 

49 

32 

264 

187 

390 

265 

601 

398 

57 

41 

267 

191 

440 

293 

601 

399 

63 

67 

268 

191 

448 

299 

607 

403 

70 

51 

269 

192 

459 

306 

621 

413 

71 

51 

273 

461 

307 

622 

414 

73 

53 

275 

196 

464 

308 

623 

414 

93 

63 

276 

197 

465 

309 

624 

415 

96 

66 

277 

198 

468 

313 

625 

415 

98 

67 

281 

201 

469 

313 

625 

416 

100 

390 

289 

205 

475 

318 

643 

429 

108 

74 

292 

206 

476 

318 

645 

430 

111 

293 

206 

480 

322 

648 

432 

119 

82 

297 

223 

481 

324 

648 

433 

121 

83 

297 

234 

482 

324 

650 

399 

123 

84 

305 

212 

498 

331 

655 

437 

138 

94 

306 

212 

499 

331 

656 

437 

148 

99 

308 

212 

500 

333 

657 

437 

149 

99 

313 

215 

505 

334 

657 

438 

153 

103 

326 

224 

507 

335 

659 

438 

158 

106 

328 

226 

513 

341 

659 

439 

160 

,  106 

332 

229 

518 

343 

660 

439 

161 

107 

334 

224 

521 

345 

673 

162 

335 

234 

528 

350 

685 

446 

163 

204 

335 

235 

533 

353 

689 

449 

164 

204 

344 

353 

535 

353 

697 

455 

172 

112 

344 

354 

536 

353 

701 

458 

176 

115 

346 

264 

541 

357 

705 

460 

179 

118 

347 

252 

544 

710 

464 

180 

118 

349 

238 

553 

712 

665 

182 

120 

356 

240 

558 

367 

715 

468 

211 

135 

357 

565 

715 

469 

230 

161 

359 

231 

571 

374 

718 

470 

232 

360 

236 

578 

382 

729 

480 

237 

360 

243 

581 

385 

730 

481 

238 

167 

361 

244 

587 

394 

744 

492 

239 

167 

362 

244 

594 

335 

754 

J231 

241 

168 

369 

249 

595 

392 

756 

501 

•Hta 

-Jin 

374 

252 

598 

397 

759 

503 

•^^•_ 

375 

253 

599 

397 

